Hackers rarely gain access to a computer or business network simply by "breaking through" a firewall in one dramatic step. Most successful compromises begin with something much more ordinary: a stolen password, phishing email, unpatched application, exposed remote-access service, malicious download, misconfigured cloud account, or a user being tricked into granting access.

Once attackers obtain an initial foothold, they may attempt to increase their privileges, steal additional credentials, move to other computers, access servers and cloud services, copy sensitive information, establish persistent access, or deploy ransomware.

Understanding how attackers typically get in is therefore one of the most important parts of cybersecurity.

This article explains the most common initial-access techniques, what can happen after the first compromise, warning signs to watch for, and practical defensive measures for businesses and individual users.

1. Phishing Emails

Phishing remains one of the most common methods used to obtain unauthorized access.

An attacker sends an email designed to appear as though it came from a legitimate organization or trusted person.

Examples may impersonate:

• Microsoft
• Google
• A bank
• A courier company
• A customer or supplier
• A company's HR department
• An IT administrator
• A senior employee
• A cloud service
• A tax or government department

The message usually tries to convince the recipient to perform an action.

For example:

"Your Microsoft 365 password expires today. Click here to keep your account active."

The link may lead to a fake login page.

The victim enters:

Email address → Password → MFA information

The attacker can then attempt to use those credentials against the real service.

Common phishing objectives

Attackers may try to:

• Steal usernames and passwords
• Obtain Microsoft 365 credentials
• Obtain Google Workspace credentials
• Capture MFA codes
• Deliver malware
• Convince users to run malicious files
• Change banking information
• Obtain confidential business information
• Take over email accounts

More targeted phishing attacks are commonly called spear phishing.

2. Malicious Email Attachments

Instead of stealing credentials directly, attackers may attempt to convince the recipient to open a malicious attachment.

Potentially dangerous files can include:

• Executable files
• Scripts
• Archive files
• Disk images
• Shortcut files
• Documents containing malicious content
• Password-protected archives used to evade scanning

A malicious file may install malware or download additional malicious components.

Depending on the attack, this can lead to:

• Credential theft
• Information theft
• Remote access
• Ransomware
• Browser-data theft
• Persistence on the computer

Users should therefore treat unexpected attachments carefully—even when the message appears to come from someone they know.

A legitimate person's email account may itself have been compromised.

3. Stolen Usernames and Passwords

Attackers do not always need to exploit a technical vulnerability.

Sometimes they simply log in.

Passwords may be obtained through:

• Phishing
• Malware
• Information-stealing malware
• Data breaches
• Keyloggers
• Fake login pages
• Password reuse
• Social engineering
• Previously compromised devices

If a password used on one website is reused for Microsoft 365, VPN, RDP, Google Workspace, banking, hosting, or another important service, one breach can potentially lead to several account compromises.

This is why unique passwords are extremely important.

4. Credential Stuffing

Credential stuffing occurs when attackers take usernames and passwords obtained from previous breaches and automatically test them against other services.

For example, suppose a user has used the same email address and password for:

• An online shopping website
• Webmail
• Microsoft 365
• A company portal
• Cloud storage

If one service is compromised, attackers may try those credentials against the others.

Credential stuffing succeeds primarily because people reuse passwords.

Defense

Use:

• Unique passwords
• A reputable password manager
• Multi-factor authentication
• Login alerts
• Risk-based sign-in controls where available

5. Brute-Force Password Attacks

A brute-force attack attempts many password combinations until the correct password is discovered.

Attackers may target:

• RDP
• VPNs
• Web portals
• Email accounts
• FTP services
• SSH
• Routers
• NAS devices
• Administrative interfaces

Weak passwords make these attacks substantially easier.

Passwords such as:

admin123

company123

password123

or predictable variations of company names, employee names, phone numbers, and years should never be used.

6. Password Spraying

Password spraying is slightly different from traditional brute forcing.

Instead of trying thousands of passwords against one account, an attacker tries a small number of commonly used passwords against many accounts.

For example:

Welcome123

might be tested against hundreds of usernames.

This approach may reduce the likelihood of triggering account lockout mechanisms.

Organizations should therefore monitor authentication systems for unusual login patterns across multiple accounts.

7. Exposed Remote Desktop Protocol (RDP)

Remote Desktop is extremely useful for administrators and remote workers, but poorly secured internet-facing RDP can create significant risk.

Attackers continuously scan the internet looking for exposed remote-access services.

If RDP is directly accessible from the internet, attackers may attempt:

• Password guessing
• Credential stuffing
• Password spraying
• Exploitation of vulnerabilities
• Use of previously stolen credentials

A compromised RDP account can provide direct interactive access to a Windows computer or server.

Safer approach

Where possible, avoid exposing RDP directly to the public internet.

Consider using:

Internet → Firewall/VPN or RD Gateway → Authentication/MFA → RDP Server

Additional protections may include:

• Network Level Authentication
• MFA
• Strong passwords
• Account lockout policies
• Restricted source IP addresses
• VPN access
• RD Gateway
• Firewall rules
• Continuous log monitoring

8. VPN Account Compromise

VPNs are intended to protect remote connectivity, but compromised VPN credentials can give an attacker a route into an internal network.

Attackers may obtain VPN access through:

• Stolen passwords
• Password reuse
• Phishing
• Credential-stealing malware
• Vulnerable VPN appliances
• Outdated firmware
• Misconfiguration

Organizations should keep VPN gateways updated and use MFA whenever supported.

9. Unpatched Software Vulnerabilities

Software vulnerabilities are another major entry point.

Attackers may exploit weaknesses in:

• Windows
• Linux
• Web servers
• VPN appliances
• Firewalls
• Routers
• Browsers
• WordPress
• Plugins
• Remote-access software
• Database servers
• Email servers
• NAS devices
• Business applications

Once a vulnerability becomes publicly known, attackers may rapidly begin scanning for vulnerable systems.

A business that delays critical security updates may therefore remain exposed even when a fix is already available.

10. Zero-Day Vulnerabilities

A zero-day vulnerability is a security weakness for which effective protection or a vendor patch may not yet be broadly available when exploitation begins.

Zero-day attacks can be particularly dangerous because traditional patching alone may not immediately solve the problem.

Organizations can reduce risk through defense-in-depth controls such as:

• Endpoint detection and response
• Network segmentation
• Application control
• Least privilege
• Email filtering
• Behavioral monitoring
• Web filtering
• Attack-surface reduction
• Strong authentication

No single security product guarantees protection against every zero-day attack.

11. Malware and Trojan Horses

A Trojan is malicious software disguised as something useful or legitimate.

Examples might include fake:

• PDF utilities
• Software cracks
• Activation tools
• Browser extensions
• Invoice viewers
• Drivers
• System cleaners
• Video players
• Updates
• Remote-support utilities

After execution, the malware may establish communication with attacker-controlled infrastructure.

The attacker may then attempt to steal information or download additional malicious components.

12. Information-Stealing Malware

Information stealers, often called infostealers, are designed to collect valuable information from infected systems.

Depending on the malware and the system, targeted data can include:

• Saved browser passwords
• Cookies
• Authentication tokens
• Cryptocurrency wallet information
• Email credentials
• FTP credentials
• Application credentials
• Autofill information
• System information

This creates an important security issue:

Changing only the password may not always be sufficient after a compromised device is discovered.

Existing sessions and authentication tokens may also need to be revoked.

13. Remote Access Trojans (RATs)

A Remote Access Trojan can allow an attacker to remotely interact with an infected computer.

Depending on its capabilities and privileges, a RAT may allow activities such as:

• Running commands
• Downloading files
• Uploading files
• Capturing screenshots
• Monitoring activity
• Stealing information
• Installing additional malware

RAT infections frequently originate from phishing, malicious downloads, pirated software, or social engineering.

14. Fake Technical Support and Remote-Access Scams

Not every attacker needs sophisticated malware.

Sometimes the victim is convinced to install legitimate remote-access software.

A scammer may claim to represent:

• Microsoft
• A bank
• An antivirus company
• An ISP
• An accounting software company
• A government department
• Technical support

The victim may then be asked to install a remote-support application and provide an access code.

At that point, the victim has effectively granted the attacker remote access.

Important rule

Never provide remote-access credentials or session codes to an unsolicited caller.

15. Malicious or Compromised Websites

A website can also become part of an attack.

Users may encounter:

• Fake login pages
• Malicious advertisements
• Fake CAPTCHA instructions
• Fake browser updates
• Fake antivirus warnings
• Malicious downloads
• Compromised legitimate websites

One increasingly dangerous technique involves a page displaying instructions such as:

"Verification required. Press these keys and paste this command."

Users should never execute commands supplied by an unknown website merely to prove that they are human.

16. Pirated and Cracked Software

Cracked software is a significant malware-delivery risk.

Attackers know that users downloading pirated applications may expect antivirus warnings or unusual installation instructions.

This makes cracks and activators attractive places to hide:

• Trojans
• Password stealers
• Cryptominers
• Backdoors
• Ransomware loaders
• Remote-access malware

Software should be downloaded from the original vendor or another verified source whenever possible.

17. Malicious Browser Extensions

Browser extensions can have powerful permissions.

Depending on the permissions granted, an extension may potentially:

• Read webpage content
• Modify webpages
• Observe browsing activity
• Access information entered into websites
• Redirect searches
• Inject advertisements

Only install necessary extensions from trusted developers and periodically review installed extensions.

Remove extensions that are no longer required.

18. MFA Attacks

Multi-factor authentication significantly improves account security, but attackers may attempt to bypass or abuse it.

Common techniques include:

MFA Fatigue

An attacker repeatedly sends authentication prompts hoping that the user eventually approves one.

Phishing Proxies

More sophisticated phishing infrastructure may attempt to capture authentication sessions rather than only passwords.

Social Engineering

An attacker may contact the victim and claim:

"You will receive an authentication request. Please approve it so we can fix your account."

Never approve an MFA request that you did not initiate.

19. Session Cookie and Authentication Token Theft

Modern websites often use authentication cookies or tokens to keep users signed in.

If malware steals a valid authentication session, an attacker may sometimes gain access without immediately needing to enter the user's password again.

This is why incident response after credential-stealing malware may include:

• Changing passwords
• Signing out active sessions
• Revoking authentication tokens
• Reviewing MFA methods
• Checking recovery information
• Reviewing account activity

20. Router and Firewall Compromise

Routers and firewalls are critical because they control network traffic.

Attackers may target devices that have:

• Default passwords
• Weak administrator passwords
• Outdated firmware
• Exposed management interfaces
• Unnecessary remote administration
• Known vulnerabilities

A compromised router could potentially allow attackers to manipulate traffic or change DNS settings.

Administrators should regularly review:

• Firmware versions
• DNS settings
• Administrator accounts
• Remote-management settings
• Firewall rules
• Port forwarding
• VPN configurations

21. Wi-Fi Attacks

Wireless networks can also provide an entry point when configured poorly.

Risk increases with:

• Weak Wi-Fi passwords
• Old security standards
• Shared passwords
• Unsecured guest networks
• Rogue access points
• Outdated router firmware

Modern Wi-Fi security such as WPA2 or WPA3 should be used where supported.

Business guest Wi-Fi should generally be isolated from sensitive internal systems.

22. Man-in-the-Middle Attacks

In a Man-in-the-Middle attack, an attacker attempts to position themselves between communicating systems.

The attacker may try to:

• Observe traffic
• Redirect communication
• Manipulate traffic
• Steal authentication information

Encrypted protocols such as HTTPS substantially reduce many interception risks, but users should still be cautious with untrusted networks.

23. USB and Removable Media

USB devices can also introduce malware.

Potential scenarios include:

• Infected USB drives
• Unknown USB devices
• Malicious USB hardware
• Files copied from compromised computers
• Autorun-related attacks on older systems

Organizations handling sensitive systems should define clear removable-media policies.

24. Supply Chain Attacks

Sometimes attackers do not attack the target organization directly.

Instead, they compromise a trusted supplier.

Potential targets include:

• Software vendors
• IT service providers
• Managed service providers
• Update infrastructure
• Development environments
• Cloud providers
• Business partners

The compromised supplier may then become the path into multiple customers.

This is known as a supply chain attack.

25. Insider Threats

Not every security incident originates outside the organization.

Employees, contractors, vendors, or former staff may intentionally or accidentally create security problems.

Examples include:

• Copying confidential files
• Sharing passwords
• Installing unauthorized applications
• Sending information to personal email accounts
• Misusing administrator access
• Leaving accounts active after employment ends

Organizations should follow the principle of least privilege.

Users should receive only the permissions required for their work.

What Happens After Hackers Gain Initial Access?

Getting into one computer is often only the beginning.

Attackers may proceed through several stages.

Stage 1 — Initial Access

The attacker obtains access through phishing, stolen credentials, malware, vulnerabilities, or another technique.

Stage 2 — Persistence

The attacker attempts to maintain access even after a restart or password change.

Stage 3 — Privilege Escalation

The attacker attempts to obtain higher-level privileges such as local administrator or domain administrator.

Stage 4 — Credential Access

Passwords, hashes, browser sessions, tokens, and other credentials may be targeted.

Stage 5 — Discovery

The attacker investigates the environment.

They may identify:

• Servers
• Workstations
• Shared folders
• User accounts
• Applications
• Domain infrastructure
• Backup systems

Stage 6 — Lateral Movement

The attacker attempts to move from one compromised computer to additional systems.

For example:

Employee PC → File Server → Application Server → Domain Resources

Stage 7 — Data Collection

Sensitive information may be collected.

Stage 8 — Data Exfiltration

Information may be transferred outside the organization.

Stage 9 — Impact

Depending on the attacker's objective, the final impact might include:

• Ransomware
• Data theft
• Account takeover
• Financial fraud
• Business email compromise
• Destruction of information
• Service disruption

How Can You Tell Whether a Computer May Have Been Compromised?

Possible warning signs include:

• Unexpected antivirus alerts
• Unknown programs
• New administrator accounts
• Unexpected remote-access software
• Unusual CPU usage
• Unexpected network traffic
• Browser redirects
• Security tools being disabled
• Unexplained firewall changes
• Unknown startup applications
• Files becoming encrypted
• Unusual scheduled tasks
• Unexpected PowerShell activity
• Login alerts from unknown locations
• Password-reset emails you did not request
• MFA prompts you did not initiate

One symptom alone does not necessarily prove compromise, but unusual combinations should be investigated.

How Can You Tell Whether a Network May Have Been Compromised?

Administrators should look for anomalies such as:

• Logins at unusual times
• Authentication from unexpected locations
• Multiple failed login attempts
• New administrator accounts
• Unexpected firewall rules
• Unknown VPN sessions
• Unusual DNS requests
• Large unexplained outbound transfers
• Connections to suspicious external systems
• Security tools unexpectedly disabled
• New services or scheduled tasks
• Unusual PowerShell or command-line activity

Centralized logging greatly improves the ability to detect these patterns.

How to Reduce the Risk of Hacker Access

Security works best as multiple layers rather than one product.

A practical defensive architecture might look like:

Internet

↓

Firewall / Secure Gateway

↓

VPN or Secure Remote Access

↓

MFA

↓

Endpoint Protection / EDR

↓

Patched Operating Systems and Applications

↓

Restricted User Permissions

↓

Network Segmentation

↓

Protected Backups

↓

Monitoring and Incident Response

Organizations should prioritize strong authentication, timely patching, endpoint protection, email security, secure remote access, least privilege, user awareness, network segmentation, logging, and tested backups.

Important Security Practices

Use Multi-Factor Authentication

Enable MFA for important services including:

• Microsoft 365
• Google Workspace
• VPN
• Remote-access portals
• Hosting control panels
• Cloud services
• Administrator accounts

Use Unique Passwords

Never reuse important passwords.

A password manager can make unique credentials much easier to maintain.

Patch Systems Regularly

Keep operating systems, browsers, applications, routers, firewalls, VPN appliances, WordPress installations, plugins, and other internet-facing systems updated.

Restrict Administrator Rights

Ordinary users generally should not operate with permanent administrator privileges unless their role requires them.

Protect Remote Access

Avoid unnecessary public exposure of RDP, SSH, database servers, NAS administration interfaces, and similar services.

Maintain Backups

Follow a backup strategy that includes multiple copies and, where appropriate, an offline, immutable, or otherwise isolated copy.

Most importantly, backups should be tested periodically.

A backup that cannot be restored is not an effective recovery solution.

Example of a Layered Business Security Model

Consider a small organization with:

• 25 employees
• Windows PCs
• Windows Server
• Microsoft 365
• Accounting applications
• Shared folders
• Remote users

A stronger architecture could be:

Internet

↓

Business Firewall

↓

VPN / RD Gateway + MFA

↓

Segmented Internal Network

↓

Windows Server

↓

Restricted User Accounts

↓

Endpoint Security / EDR

↓

Cloud + Offline/Immutable Backup

↓

Centralized Logging and Monitoring

This approach assumes that individual security controls can fail and therefore uses additional controls to limit the damage.

Frequently Asked Questions (FAQ)

1. How do hackers most commonly get into computers?

Common entry methods include phishing, stolen passwords, malware, malicious downloads, exposed remote-access services, and exploitation of unpatched vulnerabilities.

2. Can a hacker access my computer just by knowing my email address?

An email address alone normally does not provide computer access. However, attackers can use it for phishing, password guessing, credential stuffing, and account-recovery attacks.

3. Can hackers get into a computer without installing malware?

Yes. Stolen credentials can allow attackers to log into email, VPN, cloud applications, remote-access systems, or other services without installing traditional malware.

4. Is RDP dangerous?

RDP is a legitimate administrative technology. Risk increases when it is exposed directly to the internet or protected by weak credentials. VPNs, RD Gateway, MFA, NLA, firewall restrictions, and monitoring can substantially improve security.

5. Can hackers bypass MFA?

Some attacks can defeat or circumvent poorly implemented MFA, particularly through social engineering, MFA fatigue, session theft, or sophisticated phishing. MFA still provides a major security improvement and should generally be enabled.

6. Can antivirus stop hackers?

Antivirus is one security layer, not a complete security strategy. Strong authentication, patching, firewalls, endpoint protection, secure configuration, backups, monitoring, and user awareness are also important.

7. Can hackers enter through Wi-Fi?

Potentially. Weak passwords, obsolete wireless security, vulnerable routers, and poor network segmentation can increase risk.

8. Can opening an email infect my computer?

Modern email clients provide significant protections, and merely viewing an ordinary email usually does not cause infection. Risk increases when users open malicious attachments, follow malicious links, execute downloaded files, or when an unpatched vulnerability is exploited.

9. Can hackers use AnyDesk or other remote-support software?

Legitimate remote-support tools can be abused when victims are tricked into installing them or providing access credentials. Never grant remote access to an unsolicited caller.

10. How do hackers steal passwords?

Common techniques include phishing, malware, keylogging, information stealers, breached databases, social engineering, and fake login pages.

11. What is credential stuffing?

Credential stuffing is the automated testing of previously stolen username/password combinations against other websites or services.

12. What is password spraying?

Password spraying involves trying a small number of commonly used passwords against many accounts rather than many passwords against one account.

13. What is lateral movement?

Lateral movement occurs when an attacker who has compromised one system attempts to access additional systems within the same environment.

14. What is privilege escalation?

Privilege escalation is the process of obtaining permissions greater than those initially available to the attacker, such as moving from a standard account to administrator privileges.

15. Can hackers steal browser passwords?

Malware running with sufficient access may target credentials, cookies, tokens, autofill information, and other browser data. Browser and operating-system protections reduce risk but cannot make a compromised endpoint completely safe.

16. What should I do if I accidentally clicked a phishing link?

Do not enter credentials. If you already entered a password, change it promptly from a trusted device, revoke active sessions where possible, verify MFA and recovery settings, and report the incident to your administrator or service provider.

17. What should I do if I accidentally installed suspicious software?

Disconnecting the affected device from the network may help contain an active compromise. Have the system investigated with appropriate security tools and change potentially exposed credentials from a known-clean device.

18. Should RDP port 3389 be open to the internet?

Directly exposing RDP to the public internet should generally be avoided. A VPN, RD Gateway, MFA, source-IP restrictions, and other protective controls are safer approaches.

19. Does changing my password remove a hacker?

Not necessarily. An attacker may have persistence, additional compromised accounts, stolen authentication tokens, malware, or another access path. A suspected compromise requires investigation rather than only a password change.

20. What is the best protection against hackers?

There is no single best product. The strongest approach is defense in depth: MFA, unique passwords, patching, secure remote access, endpoint protection, least privilege, network segmentation, monitoring, user education, and tested backups.

Conclusion

Hackers typically gain access by exploiting a combination of technology weaknesses and human behavior.

The initial compromise may begin with something as simple as:

Phishing Email → Stolen Password → Account Access

or:

Exposed Remote Service → Compromised Credentials → Server Access

or:

Malicious Download → Malware → Credential Theft → Network Access

The more dangerous attacks then progress through:

Initial Access → Persistence → Privilege Escalation → Credential Theft → Lateral Movement → Data Theft or Ransomware

For businesses, cybersecurity should therefore not focus only on antivirus software. Protecting identities, endpoints, email, remote access, servers, networks, cloud accounts, and backups as interconnected layers provides substantially stronger protection.

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