A computer virus is a type of harmful program that gets onto your computer without your permission. It can slow everything down, steal your information, or even lock you out of your files.

The tricky thing is that many viruses work quietly in the background. You might not notice anything at first. But here are the most common warning signs to watch for.

Sign 1: Your Computer Is Much Slower Than Usual

If your computer has suddenly become very slow — pages take a long time to load, programs take ages to open, or the whole machine feels sluggish — this can be a sign of a virus.

Some viruses use your computer’s power to do things in the background (like mining cryptocurrency or sending spam emails) without you knowing.

What to check: Is this slowness new? Did it start recently? If yes, run a virus scan.

Sign 2: Pop-Up Advertisements Are Appearing

If you are seeing a lot of pop-up ads — especially ones advertising things you never searched for, or ones that appear even when you are not browsing the internet — your computer likely has a type of virus called adware.

Some of these pop-ups may look like official warnings from Microsoft or your bank. They are not. Do not call any phone number shown in a pop-up.

Sign 3: Your Browser’s Homepage Has Changed

If you open your browser (like Chrome or Edge) and the homepage is different from what you set — perhaps showing a search engine you do not recognise — something has changed your settings without permission. This is often caused by a type of virus called a browser hijacker.

Sign 4: You Are Being Redirected to Strange Websites

You click a normal link or type in a website address, but you end up on a completely different website. This is a classic sign of a browser hijacker virus.

Sign 5: Programs You Did Not Install Are Appearing

If you notice programs or applications on your computer that you do not remember installing, they may have come bundled with something else you downloaded, or been installed by a virus.

Check your list of installed programs and remove anything you do not recognise. On Windows: Settings → Apps → Installed Apps

Sign 6: Your Friends Are Receiving Strange Emails From You

If someone tells you they received a strange email from your address — one you did not send — your email account or computer has likely been compromised.

Do this immediately:

1. Change your email password right away
2. Check if the virus has access to other accounts
3. Run a virus scan

Sign 7: Your Antivirus Has Been Disabled or Is Not Working

Some clever viruses try to turn off your antivirus program so it cannot detect them. If your antivirus has stopped working or you cannot open it, that is a very serious warning sign.

What to Do If You Think You Have a Virus

Step 1: Do not panic. Most viruses can be removed.

Step 2: Stop what you are doing. Do not enter any passwords or bank details until the computer is clean.

Step 3: Run a scan with a trusted antivirus program. If you have one installed, open it and run a full scan. If you do not have one, download Malwarebytes — it has a free version that is very effective.

Step 4: Follow the instructions. The antivirus will tell you what it found and help you remove it.

Step 5: Change your passwords on important accounts (email, bank) after the computer is clean.

How to Prevent Viruses in Future

• Keep your antivirus programme up to date
• Keep Windows and your browser updated — updates fix security holes
• Do not click links in emails from people you do not know
• Do not download programmes from websites you do not trust
• Be careful with USB sticks from unknown sources

Our recommendation for antivirus: