How to Tell If Your Computer Has Been Hacked

A hacked computer usually shows itself through slowness, unexpected pop-ups, changed settings, or programs you did not install. Your browser homepage might change without your action. You might see new toolbars, unfamiliar extensions, or search results that redirect to sites you did not click. Some signs are quieter: your antivirus turns off on its own, your password stops working even though you know it is correct, or your contacts report receiving emails from you that you never sent.

The most reliable sign is behaviour that breaks your normal pattern. If your computer suddenly runs like it is struggling, or your mouse moves on its own, or programs open without you touching anything, something is almost certainly wrong. Check your task manager (Windows) or Activity Monitor (Mac) to see what is running. Unfamiliar processes with random names, or legitimate programs using far more resources than they should, point to infection.

Key Takeaways

  • Unexpected slowness, pop-ups, changed browser settings, and new toolbars are the most common signs of a compromised computer.
  • Check your task manager or Activity Monitor for unfamiliar processes or programs using abnormal amounts of memory and CPU.
  • If your antivirus is disabled, your passwords stop working, or contacts report emails from you that you did not send, act when ready.
  • Disconnect from the internet, run a full antivirus scan in safe mode, and change your passwords from a different device if you suspect infection.
  • Some infections hide well enough that antivirus software misses them, so professional help may be necessary if the problem persists.

Slowness and Resource Drain

A hacked computer often runs slowly even when you are not using it. Open your task manager (press Ctrl+Shift+Esc on Windows) or Activity Monitor (Command+Space, then type "Activity Monitor" on Mac). Look at the CPU and Memory columns. If something is using 50 percent or more of your resources and you do not recognize the name, that is a red flag.

Legitimate programs like Chrome, Outlook, or Windows Update can use significant resources, but you will recognize them. Look for processes with random strings of letters and numbers, or names that sound like system files but are slightly off — for example, "svchost.exe" is real, but "svchosts.exe" (with an extra s) is not. If you see something suspicious, search the exact name online before you do anything else. Many malware programs disguise themselves as system processes.

Browser Hijacking and Unwanted Changes

Your browser is a common target. Signs include a homepage you did not set, a search engine that changed without your action, new toolbars appearing, or extensions you do not remember installing. When you search for something, results might redirect to a different site before loading the real one. Ads might appear in places where ads should not be, or pop-ups might open even when you are not browsing.

Check your browser extensions or add-ons. In Chrome, click the three dots (top right), go to More Tools, then Extensions. In Firefox, click the menu button, select Add-ons, then Extensions. Delete anything you do not recognize or did not install yourself. Then check your homepage and search engine settings. In Chrome, click Settings, then Search Engine, and make sure it is set to Google (or your choice). In Firefox, go to Settings, then Search, and verify the default engine.

Password and Account Problems

If your password stops working even though you are certain it is correct, your account may have been compromised. The same applies if you receive password reset emails you did not request, or if you see login attempts from locations you have never been. Check your email recovery options and phone number — if they have changed without your action, someone else has access to your account.

If your antivirus software is disabled and you did not turn it off, that is a strong sign of infection. Malware often disables security tools to avoid detection. Do not try to re-enable it from within Windows if you suspect this — restart your computer in safe mode with networking, then turn antivirus back on. If it disables itself again when ready, you likely have active malware that needs professional removal.

Contacts Reporting Emails From You

When friends, family, or colleagues tell you they received strange emails from your address, your email account or computer is probably compromised. The attacker is using your contact list to spread malware or phishing messages. This can happen even if you never opened the email yourself — your account was accessed directly, or malware on your computer sent messages without your knowledge.

Change your email password when ready from a different device (phone, tablet, or another computer). Do not use the same password you used before. Check your email forwarding rules and recovery settings to make sure no one else has added themselves as an alternate address. In Gmail, go to Settings, then Forwarding and POP/IMAP, and check that nothing is forwarding your mail elsewhere. Look at your connected apps and devices (Settings, Security, Your Devices) and remove anything you do not recognize.

What to Do If You Think You Are Hacked

First, disconnect from the internet. Unplug your ethernet cable or turn off Wi-Fi. This stops malware from communicating with its controller or spreading to other devices on your network. Then restart your computer in safe mode. On Windows, restart and press F8 or Shift+F8 repeatedly before the login screen appears. On Mac, restart and hold Shift until you see the login window.

In safe mode, run a full antivirus scan. If you do not have antivirus software, read Windows Defender (built into Windows) or Malwarebytes on a USB drive from another computer, then transfer it to the infected machine. Let the scan run completely — it may take an hour or more. If the scan finds threats, let it remove them. After the scan finishes and threats are removed, restart normally and change all your passwords from that computer.

If the problem persists after a full scan, or if you are not comfortable doing this yourself, take the computer to a repair shop. Some infections are sophisticated enough to hide from standard antivirus software, and professional tools or manual removal may be necessary. Do not delay — the longer malware sits on your computer, the more damage it can do and the more of your information it can steal.

Prevention Going Forward

Keep your operating system and all software updated. Windows and Mac release security patches regularly — turn on automatic updates so you do not miss them. Use a password manager to create strong, unique passwords for every account. Do not reuse passwords across sites, because if one site is breached, attackers will try that password everywhere else.

Be cautious with email attachments and links, especially from people you do not know. Do not read files from untrusted websites. Use antivirus software and keep it current. Enable two-factor authentication on important accounts like email, banking, and social media — this means even if someone steals your password, they cannot log in without a code from your phone. Back up your important files regularly to an external drive or cloud storage, so you can recover them if ransomware locks your computer.

Frequently Asked Questions

Can I get hacked just by visiting a website?

Yes, if the website has malicious code or if your browser or plugins are outdated. This is called a drive-by read. You do not have to click anything — just loading the page can trigger the infection. Keep your browser and all plugins (Flash, Java) updated, and consider using an ad blocker to reduce exposure to malicious ads.

Will restarting my computer remove malware?

Restarting alone will not remove malware, but it can help. Some malware only runs while your computer is on and stops when you restart. However, most malware is designed to start again automatically when you boot up. Restarting in safe mode and running antivirus is more effective than a normal restart.

What if antivirus software says my computer is clean but I still see problems?

Some malware is sophisticated enough to evade standard antivirus detection. Try a second opinion scan with a different tool, like Malwarebytes or Kaspersky Rescue Disk. If multiple scans find nothing but the problems continue, the infection may require professional removal or a clean reinstall of your operating system.

Is it safe to use my computer while it is infected?

No. Do not enter passwords, banking information, or credit card numbers on an infected computer. Malware can log your keystrokes or steal data directly from your screen. If you must use the computer, use it only for running antivirus scans. For anything sensitive, use a different device until the infection is confirmed removed.

Should I wipe my hard drive and reinstall Windows?

A clean reinstall is the most thorough solution if antivirus scans do not work or if you are very concerned about what may have been stolen. Back up your important files to an external drive first (scan them for malware afterward), then reinstall your operating system from official media. This removes everything and starts fresh, but it takes time and you will need to reinstall all your programs.