How to tell if your computer has a virus
Almost every machine that arrives in our workshop "with a virus" has something wrong with it — but only some of them are actually infected. Knowing the difference saves you money, because the fix for a failing hard drive is not the fix for adware.
Here are the signs that genuinely suggest malware, the ones that usually don't, and what to do before anything else.
Signs that genuinely suggest an infection
Malware wants to do something: show you adverts, steal credentials, mine currency, or encrypt your files. Each of those leaves traces.
- Browser pop-ups or adverts appearing outside the browser, or on pages that never had them
- Your homepage or search engine changed and changes back when you fix it
- New toolbars, extensions or programs you did not install
- Antivirus or Windows Update has been disabled and won't switch back on
- The machine is slow and the fan is running hard even when idle (a sign of currency mining)
- Friends receiving messages or emails from you that you did not send
- Files renamed with an unfamiliar extension, plus a ransom note text file — this is ransomware, act immediately
Symptoms people blame on viruses that usually aren't
A lot of what looks like infection is ordinary hardware or software wear.
- General slowness building up over years — usually a failing or full hard drive, or too many startup programs
- Random shutdowns and freezes — commonly overheating from dust-clogged fans, or failing RAM
- Blue screens after an update — a driver problem far more often than malware
- Loud fan noise alone — dust and dried thermal paste
- Pop-ups only on one dodgy website — that's the website, not your computer
What to do first
Order matters here. Doing these in the wrong sequence can make recovery harder.
- If you suspect ransomware, disconnect from the network immediately and stop — do not wipe the machine
- Do not enter any passwords or banking details on the machine until it's been checked
- Run a full scan with a properly licensed antivirus product, not a random tool from a search result
- Change important passwords from a different, known-clean device
- If anything financial may have been exposed, contact your bank before anything else
Why 'free scanner' downloads make it worse
Searching for virus removal tools is genuinely dangerous. A large share of the top results are either adware bundles or outright scams that report hundreds of fake threats and then ask for payment. Some of the worst infections we clean up arrived as an attempted virus cleaner.
Use a product you already trust, or ask someone. Never install a scanner recommended by a pop-up that told you that you had a problem.
How managed protection changes the picture
On a monitored machine this whole conversation is different. Detections are reported to a technician as they happen, so infections are usually blocked and dealt with before you notice symptoms at all. The device also reports whether protection is enabled — the single most common gap on unmanaged machines is antivirus that expired and was never renewed.