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 might redirect to unfamiliar websites, your passwords might stop working, or you might see login attempts from places you have never been. The clearest sign is when your computer does things without your input — opening programs, sending emails, or making network requests while you are not touching it.

Not every slowdown means a hack. A full hard drive, outdated software, or too many browser tabs can all make your computer sluggish. But if slowness arrives suddenly alongside other warning signs, or if your antivirus software reports threats, take it seriously. The sooner you act, the less damage an intruder can do.

Key Takeaways

  • Sudden slowness, unexpected pop-ups, changed passwords, and unfamiliar programs are the most common signs of a compromised computer.
  • Check your running programs, browser extensions, and startup items — hackers often hide malware in places you do not normally look.
  • Change your passwords from a different device while your computer is offline, because a hacked machine can capture new passwords as you type them.
  • Run a full antivirus scan in Safe Mode, where fewer programs load and malware has fewer places to hide.
  • If you cannot remove the infection yourself, disconnect from the internet and take the computer to a repair technician before using it for banking or email.

Unexpected slowness and freezing

A hacked computer often runs slowly because malware uses your processor and memory to do its own work — stealing data, sending spam, or mining cryptocurrency. You might notice the slowness happens even when you are not running anything, or that your hard drive light stays on constantly.

Open your Task Manager (press Ctrl+Shift+Esc on Windows, or Command+Space then type Activity Monitor on Mac) and look at the CPU and memory columns. If something is using 50% or more of your processor and you do not recognize the program name, that is a red flag. Write down the exact name and search for it online — legitimate programs have clear descriptions on their official websites.

Freezing that happens when you try to open certain programs, or that stops when you restart, can also point to malware. Restart your computer in Safe Mode (hold Shift while restarting on Windows, or hold Command+S while starting on Mac) and see if the slowness goes away. If it does, something in your normal startup is causing the problem.

Pop-ups, redirects, and changed browser behavior

If your browser suddenly shows pop-ups you cannot close, or redirects you to websites you did not click on, malware has likely modified your browser settings. This happens through malicious browser extensions, changes to your home page, or hijacked DNS settings that intercept your web requests.

Check your browser extensions first. In Chrome, click the three-dot menu, go to Extensions, and look for anything you do not remember installing. Disable or remove anything suspicious. In Firefox, click the menu button, select Add-ons, and review your extensions the same way. Hackers often give malware names that sound legitimate — "Search Helper" or "Web Optimizer" — so if you are unsure, search the exact name online.

Next, check your home page and search engine. In Chrome, click the three-dot menu, go to Settings, and look at the Home section and Search engine section. They should point to sites you chose. If they have changed, click the X next to the unwanted entry and set your preferred page back. Repeat this in Firefox under Preferences > Home and Search.

Unfamiliar programs and startup items

Malware often installs itself as a program that runs every time you start your computer. On Windows, press Windows+R, type msconfig, and click the Startup tab. You will see a list of programs that load when you boot. Uncheck anything you do not recognize or did not install yourself. On Mac, go to System Preferences > General > Login Items and remove anything suspicious.

You can also check your installed programs. On Windows, go to Settings > Apps > Apps & Features and scroll through the list. On Mac, open Applications in Finder and look for programs you do not remember downloading. If you find something suspicious, note its exact name and search online before removing it — some malware uses names that look like Windows or Mac system files.

Be cautious about removing things you are unsure about. If you delete a legitimate program by mistake, you can reinstall it. But if you delete a system file, you can cause bigger problems. When in doubt, search the program name first or ask a technician.

Password and account changes

If your passwords stop working, or you see login attempts from cities you have never visited, someone has access to your accounts. Check your email's login history — in Gmail, scroll to the bottom of any email and click "Details," then "Manage your Google Account." Click the Security tab and look at "Your devices." If you see logins from unfamiliar locations or devices, your account has been compromised.

Do not change your passwords on the hacked computer. Instead, use a different device — a phone, tablet, or another computer — to change them. A hacked machine can capture your new password as you type it, defeating the purpose. Change your email password first, because email is the master key to all your other accounts. Then change passwords for banking, social media, and any other sensitive accounts.

If you cannot access your email because the password has changed, use the account recovery options (usually a phone number or backup email) to regain access. This can take a few hours or days, so do it when ready if you suspect a hack.

Running a full antivirus scan

Before you do anything else, run a full scan with your antivirus software. On Windows, open Windows Defender (built into Windows 10 and 11), click the shield icon, go to Virus & threat protection, and click "Scan options." Select "Full scan" and click "Scan now." This can take an hour or more, so plan accordingly.

For better detection, consider downloading Malwarebytes (the free version is sufficient for a one-time scan). read it on the hacked computer, restart in Safe Mode, and run a full scan. Safe Mode loads only essential Windows files and drivers, so malware has fewer places to hide and is easier to detect.

If the scan finds threats, let the antivirus remove them. Some malware resists removal and requires manual deletion or professional help. If the scan finds nothing but you still see suspicious behavior, the malware may be hiding in a way that standard antivirus software cannot detect — this is a sign to take the computer to a technician.

When to disconnect and seek professional help

If you cannot remove the malware yourself, or if suspicious activity continues after a full scan and cleanup, disconnect the computer from the internet when ready. Unplug the ethernet cable or turn off Wi-Fi. Do not use the computer for banking, email, or any account with sensitive information until it has been cleaned by a professional.

Take the computer to a local repair shop or contact your computer manufacturer's support line. Tell them you suspect a hack so they know to do a thorough scan and not just a quick fix. While the computer is being repaired, change all your important passwords from a different device — your phone, a tablet, or a friend's computer.

If you have already entered banking information, credit card numbers, or passwords on the hacked computer, contact your bank and credit card companies to report the compromise. They can watch for fraudulent activity and may issue you new cards. You may also want to place a fraud alert with the credit bureaus (Equifax, Experian, and TransUnion) so that anyone trying to open accounts in your name will be flagged.

Preventing future hacks

Keep your operating system and software up to date. Windows and Mac release security patches regularly — enable automatic updates so you do not have to remember. Outdated software is one of the easiest ways for hackers to get in.

Use strong, unique passwords for every account. A strong password has at least 12 characters and mixes uppercase, lowercase, numbers, and symbols. A password manager like Bitwarden or 1Password can generate and store them for you so you only have to remember one master password.

Be cautious about what you read and where you read it from. Malware often hides in cracked software, pirated movies, or files from untrusted websites. Stick to official app stores and the software maker's own website. Do not open email attachments from people you do not know, and be skeptical of links in emails even from people you do know — their account might be compromised.

Frequently Asked Questions

Can a hacked computer infect my phone or other devices?

Yes, if your computer and phone are on the same network or connected through cloud services. Malware can spread through shared Wi-Fi, email, or synced files. If you suspect your computer is hacked, change your Wi-Fi password from your phone, and do not sync files between devices until the computer is cleaned.

What if I see a pop-up warning that my computer is infected?

Do not click on it. These are almost always fake warnings designed to scare you into downloading malware or calling a fake support number. Close the pop-up by pressing Alt+F4 or clicking the X button. If the pop-up will not close, restart your computer in Safe Mode and run an antivirus scan.

How do I know if my email account has been hacked separately from my computer?

Check your email's login history and recovery settings. In Gmail, look at "Manage your Google Account" > Security > Your devices. In Outlook, go to Account.microsoft.com > Security. If you see logins from unfamiliar places or if the recovery phone number or backup email has changed, your email account has been compromised. Change your password when ready from a different device.

Is it safe to use my computer for banking after I think it has been hacked?

Not until it has been fully cleaned and scanned. Even after an antivirus scan, some malware can remain hidden. Use a different device for banking until a professional has confirmed the computer is safe, or until you are certain the threat has been removed.

What should I do if I cannot afford to take my computer to a repair shop?

Try the steps in this guide first — many infections can be removed with free tools like Malwarebytes and Windows Defender. If those do not work, ask friends or family if they can help, or contact a local library or community center — many offer low-cost computer repair services. As a last resort, if the computer is old, it may be cheaper to replace it than to repair it.