Real infection symptoms
Windows opening alone, changed homepage, programs you never installed, sudden slowness or a roaring fan doing nothing. One symptom alone can be something else; two or more together almost certainly mean trouble. And note: the best malware shows no symptoms, which is why a full scan matters even when "all is fine".
Step 1: full Defender
Windows already ships a good antivirus: go to Windows Security → Virus protection → Scan options → Full scan (takes 30-60 min, let it work). If it finds threats, choose Quarantine/Remove all and reboot. Then reopen Defender and confirm it says "No actions needed".
Step 2: free second opinion
No antivirus catches everything. Download Malwarebytes Free from its official site (beware ads imitating the download button), scan and remove. Don't pay for Premium for a one-off cleanup: the free one cleans the same; paid only adds real-time protection.
When to call a technician
If symptoms persist after Defender + Malwarebytes + clean browser, if there is ransomware asking for payment or the PC won't boot right since, stop touching things: every attempt can make it worse (and with ransomware, never pay: they often don't return files). We look at it in the free diagnosis.
FAQ
Is Windows Defender enough or do I need another antivirus?
For normal use it is. Malwarebytes Free as a one-off second opinion is the ideal complement.
Are free antiviruses safe?
The official ones (Defender, Malwarebytes, Avast/AVG from their sites) yes. Distrust anything arriving via popup ad.
Does formatting remove all viruses?
Almost all, but it's the nuclear option: try the three-step cleanup in this guide first.
Should I pay a ransomware ransom?
No: they often return nothing. Power off to avoid spreading and ask for help.
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