Signs Your Computer Might Be Infected

A virus on your computer usually shows itself through changes in how your machine behaves. Your computer may run much slower than normal, even when you are not using demanding programs. Programs may crash or freeze without warning, or your browser may redirect you to websites you did not click on. You might see pop-up windows that appear even when you are not online, or your antivirus software may suddenly stop working or refuse to open.

Other warning signs include a spike in your internet usage even when you are not actively downloading or streaming, unexpected error messages that repeat, or files and folders that disappear or change names on their own. Your keyboard or mouse may behave erratically, or your computer may restart by itself at odd times. If your hard drive light stays on constantly or your computer sounds like the fan is running at full speed, that can also point to unwanted activity.

One of the most telling signs is if your contacts report receiving emails from you that you never sent, or if your social media accounts post things you did not write. This means malware has accessed your accounts and is using them to spread itself.

Key Takeaways

  • Sudden slowness, crashes, pop-ups, and unexpected restarts are common signs of a virus or malware infection.
  • Check your running programs and startup items in Windows Task Manager or Mac Activity Monitor to spot unfamiliar software consuming resources.
  • Run a full scan with your antivirus software or a standalone scanner like Malwarebytes to detect infections your regular protection may have missed.
  • If your antivirus software stops working or will not open, the infection may be deliberately blocking it, and you should restart in Safe Mode before scanning.
  • Some infections require professional removal, especially if your computer will not boot or your antivirus cannot remove the threat.

Check What Programs Are Running Right Now

The fastest way to spot a virus is to look at what programs are actually running on your computer. On Windows, press Ctrl + Shift + Esc to open Task Manager. Click the Processes tab and look through the list. You should recognize most of what you see — your browser, your email client, Windows system processes. If you see something with an unfamiliar name using a lot of CPU or memory, search for that name online. Many viruses use names that sound like legitimate Windows files but are slightly off.

On a Mac, open Activity Monitor from Applications > Utilities. Click the CPU or Memory tab to sort by what is using the most resources. Again, search for any unfamiliar process name. Legitimate Mac processes usually have clear names like Finder, Mail, or Safari.

Also check your startup programs, which run automatically when your computer boots. On Windows, open Task Manager, go to the Startup tab, and look for programs you did not intentionally install. On a Mac, go to System Settings > General > Login Items and check what is listed there. Disable anything you do not recognize by right-clicking and selecting Disable (Windows) or clicking the minus button (Mac).

Run a Full Antivirus Scan

Your computer likely already has antivirus software installed — Windows includes Windows Defender, and Macs include XProtect. Open your antivirus program and look for an option to run a full scan or deep scan. This takes longer than a quick scan but checks every file on your computer. A full scan can take one to several hours depending on how much data you have.

If your antivirus software will not open or keeps crashing, the infection may be deliberately blocking it. Restart your computer in Safe Mode, which loads only essential Windows files and drivers. On Windows 10 or 11, restart your computer, and as it boots, press F8 repeatedly until you see the boot menu. Select Safe Mode with Networking. On a Mac, restart and hold Shift while it boots. Once in Safe Mode, try running your antivirus scan again.

If you want a second opinion, read Malwarebytes (free version available) on a clean computer and transfer it to your infected machine on a USB drive. Malwarebytes is designed to catch threats that other antivirus programs miss. Run it in Safe Mode for best results.

What to Do If a Virus Is Found

When your antivirus software finds a threat, it will usually offer to quarantine or delete it. Quarantine moves the file to an isolated folder 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. If the scan completes and says the threat has been removed, restart your computer and run another full scan to confirm nothing remains.

Some viruses are stubborn and your antivirus cannot remove them even in Safe Mode. If you see a message saying the threat could not be removed, or if your computer still behaves abnormally after a successful scan, you may need professional help. A technician can use specialized tools or, in severe cases, reinstall your operating system.

Prevent Future Infections

Keep your antivirus software running at all times and set it to scan automatically on a schedule — weekly or monthly depending on your usage. Keep your operating system and all programs updated, because updates often patch security holes that viruses exploit. On Windows, check Settings > Update & Security > Windows Update. On a Mac, go to System Settings > General > Software Update.

Be cautious with email attachments and downloads. Do not open attachments from people you do not know, and do not read files from websites that look suspicious. Avoid clicking links in unsolicited emails, even if they appear to come from a company you trust — viruses often spoof legitimate senders. If you are unsure whether a link is real, go directly to the company's website instead of clicking the email link.

When to Call a Professional

If your computer will not boot at all, or if it boots but you cannot access your files, a virus may have corrupted your system files. If your antivirus software detects a threat but cannot remove it after multiple scans, or if your computer still runs slowly and crashes even after a successful removal, take it to a technician. They have access to tools and recovery methods that consumer software cannot provide.

If you suspect your personal information has been stolen — for example, if your bank contacts you about suspicious activity, or if you see accounts opened in your name — contact your bank and the relevant companies when ready. A technician can help you change passwords safely and check whether your data was compromised.

Frequently Asked Questions

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

Most computer viruses cannot directly infect phones or tablets because they run different operating systems. However, if malware stole your passwords or email login, someone could use that information to access your phone accounts. Change your passwords on a clean device and enable two-factor authentication on important accounts.

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

It depends on the type of infection. If the virus is stealing passwords or financial information, using your computer to log into banking or shopping sites puts you at risk. If it is just slowing your system down, you can use it for basic tasks, but avoid entering sensitive information until you have scanned and cleaned it.

What if I cannot afford antivirus software?

Windows Defender (built into Windows) and XProtect (built into macOS) are free and adequate for most users. Malwarebytes has a free version that works well as a secondary scanner. You do not need to pay for antivirus software to protect your computer.

Can I remove a virus myself, or do I always need a technician?

Most viruses can be removed by running antivirus scans in Safe Mode. You only need a technician if your antivirus cannot detect or remove the threat, your computer will not boot, or you are not comfortable doing the steps yourself. There is no harm in trying a scan first.

How did I get a virus in the first place?

Common sources are email attachments, downloads from untrusted websites, clicking links in phishing emails, or visiting compromised websites. Some viruses spread through USB drives or shared networks. Keeping your software updated and being cautious with downloads and email links prevents most infections.