9 Signs Your Computer Has a Virus (and What to Do)
Real signs of malware on a Windows or Mac computer, what is probably just a slow machine, and the safe first steps to take if you suspect an infection.
Not every slow computer has a virus, and not every virus announces itself. Knowing which symptoms really suggest malware, and which are usually something duller, saves you panic and money.
Signs that deserve attention
1. Unexpected pop-ups outside the browser
Advertising windows appearing on the desktop or when no browser is open suggest unwanted software.
2. Browser homepage or search engine changed
If your browser keeps landing on a site you did not choose, or searches go through an unfamiliar engine, a hijacker is a likely cause.
3. New toolbars, extensions or programs you did not install
Check your installed programs and browser extensions for anything unfamiliar.
4. Security software disabled and cannot be turned back on
Malware often tries to stop protection from working.
5. Files missing, renamed or locked
Files with strange extensions, or a note demanding payment, point to ransomware. Disconnect from the network immediately.
6. Your accounts behave oddly
Friends receive messages you did not send, or you receive password-reset emails you did not request. That may mean an account has been compromised, which is a different problem from an infected device, though the two can overlap.
7. Constant high disk, CPU or network activity at idle
Unexplained heavy use when you are not doing anything can mean something is running in the background.
8. Very rapid battery drain and heat
A laptop that is hot and noisy while doing nothing deserves investigation, though dust and heavy updates can also cause it. See laptop overheating fixes.
9. Warnings telling you to call a number
A pop-up demanding you phone "support" is not a virus detection, but a scam attempt. See tech support scams.
What is probably not a virus
- General slowness with a full drive or old hardware. See why your laptop is slow.
- Crashes after an update or driver change.
- Fan noise during a heavy task.
- Occasional freezing from too little memory.
What to do if you suspect infection
- Do not panic or click anything in pop-ups.
- Disconnect from the internet if you see signs of ransomware or active compromise.
- Run a full scan with your system's built-in security tool, and an offline scan if available.
- Review installed programs and extensions and remove anything you do not recognise.
- Update the system and software to close the gaps.
- Change passwords from a different, clean device, starting with email and banking.
- Check bank and account activity over the coming days.
- Back up your important files if it is safe to do so, then scan the backup separately.
When to get help
Call in a professional if:
- Security tools cannot remove the problem.
- You see ransomware notes or locked files.
- You have shared banking details or let someone remote in.
- It is a work device holding sensitive data.
For realistic budgets, see virus and malware removal costs. If you let someone access your computer remotely, review how to stay safe with remote access.
Prevention that actually works
- Keep updates automatic.
- Download programs only from official sources.
- Be wary of attachments and links; see phishing emails and texts.
- Use a password manager and two-factor authentication.
- Keep regular backups so the worst case is manageable.
On Compito you can search by postcode, compare ID-verified local providers and send a request describing the symptoms. You receive an offer, accept and pay online and message the provider to agree the scope. See tech support services.
A worked example
A user notices their browser homepage has changed, a new toolbar has appeared and the laptop is slower than usual. They have not clicked anything alarming. A check of installed programs shows an unfamiliar "PDF helper", installed the same afternoon as a free converter tool. Removing the program and resetting the browser settings, followed by a full scan and updates, resolves it. The cost was an hour of their time. The cause was a bundled extra in a free download, and it shows why the source of programs matters.
Quick triage
| What you see | Probably | First step |
|---|---|---|
| Homepage and search changed | Browser hijacker | Review extensions, reset browser |
| Pop-ups on the desktop | Adware | Check installed programs |
| Ransom note, locked files | Ransomware | Disconnect, do not pay, seek help |
| Account logins you did not make | Compromised account | Change passwords, enable 2FA |
| Slow, noisy, hot | Maybe malware, often dust or clutter | Check task manager |
| Call-this-number warning | Scam page | Close it, do not call |
Common mistakes
- Running several "cleaner" tools at once, which can cause more problems.
- Paying for a program advertised in a pop-up.
- Restoring a backup without scanning it first.
- Changing passwords on the infected machine rather than a clean device.
- Ignoring the problem because the computer still works.
Phones and tablets
Signs on a phone include apps you do not remember installing, a battery that drains quickly, unexpected data use, adverts in your notifications and settings that change on their own. Remove unfamiliar apps, review which apps have unusual permissions and keep the system updated.
Children's and shared devices
Shared devices pick up unwanted software more often, especially from free games and downloads. Set up separate accounts, limit installing to an adult account and review installed programs now and then. A short conversation about free downloads is often the most effective measure.
Keeping calm
Most infections are annoying rather than catastrophic, particularly when you have a recent backup. Work methodically, avoid paying anyone who calls you first and ask for help if you are unsure.
Frequently asked questions
Can Macs get viruses?
Yes. They are targeted less often, but malware, adware and phishing affect Macs too. The same sensible habits apply.
Can a virus spread to my phone or other devices?
Some threats can move across a network or via shared accounts and files, so check the other devices and change passwords if you find an infection.
Is a factory reset the best fix?
It is often effective but heavy-handed. Back up first and reinstall only from trusted sources afterwards.