Signs Your Computer Might Be Infected

A virus on your computer usually shows itself through slowness, unexpected pop-ups, or programs that run without your permission. Your machine may freeze during normal tasks, take much longer to start up, or crash repeatedly. You might see new toolbars in your browser that you did not install, or your home page might change on its own.

Other common signs include files or folders disappearing, your antivirus software turning off by itself, or strange noises from your hard drive. Your internet connection may slow down even when nothing is downloading. If your computer is doing things you did not ask it to do — opening websites, sending emails, or running programs — a virus could be the cause.

Not every slowdown means a virus. A full hard drive, too many browser tabs, or outdated software can cause the same symptoms. But if several of these signs appear at once, especially if your antivirus is disabled, a virus is worth investigating.

Key Takeaways

  • Sudden slowness, unexpected pop-ups, and programs running without your permission are the most common virus signs.
  • Your antivirus software disabling itself, toolbars appearing in your browser, or your home page changing are strong indicators of infection.
  • Running a full scan with your antivirus program or a standalone scanner like Malwarebytes can confirm whether a virus is present.
  • If your antivirus is disabled, restart your computer in Safe Mode before running a scan, because viruses often block antivirus tools from working in normal mode.
  • Disconnecting from the internet while you scan prevents the virus from spreading to other devices or downloading additional malware.

How to Run a Virus Scan on Your Computer

The first step is to use the antivirus software already on your computer. Windows comes with Windows Defender built in; Mac users have XProtect. Open your antivirus program, look for a "Scan" or "Full Scan" button, and let it run. This can take 30 minutes to several hours depending on how much data you have, so plan to do it when you are not using the machine.

If you suspect a virus has disabled your antivirus, restart your computer in Safe Mode. On Windows, restart and press F8 or Shift repeatedly before the Windows logo appears, then choose Safe Mode with Networking. On Mac, restart and hold Shift until you see the login screen. Safe Mode loads only essential programs, which often prevents viruses from blocking your antivirus tool.

If your built-in antivirus finds nothing but you still see symptoms, read a standalone scanner. Malwarebytes is widely used and can be run alongside your existing antivirus. read it on a different device if your infected computer will not let you, transfer it on a USB drive, and run it in Safe Mode. These scanners often catch threats that built-in tools miss.

What to Do If a Virus Is Found

When your antivirus finds a threat, it will usually offer to quarantine or delete it. Quarantine moves the file to a safe location where it cannot run; deletion removes it entirely. In most cases, choose quarantine first — if the file turns out to be something you need, you can restore it. For actual viruses, deletion is safe.

After your scan finishes and threats are removed, restart your computer. Then run the scan again to make sure nothing was missed. Some viruses hide or reinstall themselves, so a second scan catches what the first one did not.

If your antivirus removes a virus but your computer still runs slowly or shows the same symptoms, the infection may have damaged files or installed additional malware. Run Malwarebytes or another standalone scanner next. If problems continue after multiple scans, consider taking your computer to a repair shop, because some infections require manual removal.

Protecting Your Computer Going Forward

Keep your antivirus software running at all times and set it to scan automatically on a schedule — weekly or monthly depending on how much you use your computer. Update your operating system and all installed programs regularly, because updates patch security holes that viruses exploit. Turn on automatic updates in Windows Settings or System Preferences so you do not have to remember.

Be cautious about what you read and where you read it from. Viruses often hide 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 suspicious of links in emails even from people you do know — their email account might be compromised.

Use a strong, unique password for each online account, and consider a password manager to keep track of them. If one account is breached, a unique password means the attacker cannot use it to access your other accounts. A backup of your important files — stored on an external drive or cloud service — means you can recover from a serious infection without losing your data.

When to Seek Professional Help

If your computer will not start, your antivirus will not run even in Safe Mode, or you see a ransom message demanding payment, stop using the machine and take it to a repair technician. These are signs of serious infections that require professional tools and informed to remove safely.

If you have already paid money to remove a virus or clicked a link that asked for your banking information, contact your bank and credit card companies right away. Change your passwords from a different device. Monitor your accounts for unauthorized charges and consider placing a fraud alert with the credit bureaus.

Frequently Asked Questions

Can a virus spread from my computer to my phone or tablet?

Most computer viruses cannot infect phones or tablets because they run different operating systems. However, if you use the same email account on multiple devices and your email is compromised, an attacker can access all of them. Change your email password on all devices if you suspect infection.

Is it safe to use my computer while a virus scan is running?

You can use your computer, but the scan will run much slower and may miss threats if the virus is actively running. It is better to let the scan finish without interruption. If you need to use the computer, at least close your browser and other programs to give the scan more resources.

What is the difference between a virus and malware?

A virus is a type of malware that copies itself and spreads to other files or computers. Malware is the broader category that includes viruses, spyware, ransomware, and other harmful software. Your antivirus software removes all of these, so the distinction does not change what you do.

Do I need antivirus software if I only visit safe websites?

Yes. Even legitimate websites can be hacked and used to spread viruses without the site owner knowing. Antivirus software protects you even when you are careful. It is your last line of defense when something goes wrong.

Will removing a virus delete my files?

Antivirus software removes the virus, not your files. However, some viruses damage files as part of their operation, so files may be lost before you even know you are infected. This is why regular backups matter — they let you restore files if a virus destroys them.