Not every slow computer or weird pop-up means you have a virus, but there are some clear warning signs that something isn't right. If you're seeing any of these, it's worth looking into sooner rather than later.

The Classic Warning Signs

Your computer suddenly runs much slower than usual, even after a restart. Programs open on their own or crash without explanation. You see pop-up ads on your desktop — not in a browser, but appearing over your regular programs. Your browser homepage changed without you doing it, or you're getting redirected to websites you didn't click on. New toolbars or programs appeared that you never installed.

What to Do First

Don't panic, and don't download the first "free virus removal" tool that comes up in a search — a lot of those are scams themselves. Start with what you already have.

Open Windows Security from the Start menu, go to "Virus & threat protection," and run a Full Scan. This uses Windows Defender, which is built into your system and genuinely effective. Let it run — it takes a while but checks everything.

As a second pass, download Malwarebytes Free from malwarebytes.com. It catches things that traditional antivirus sometimes misses, particularly adware and browser hijackers.

When It's More Serious

Some infections dig in deeper than a basic scan can reach. If your computer is still acting up after running both scans, if you can't open your antivirus at all, or if you're seeing ransomware messages demanding payment, those need professional attention.