🛡️ Viruses & Security

How to Know If Your Computer Has a Virus: 12 Warning Signs

✍️ Darren — Laptop Repairs Okehampton 📅 Jan 2026 ⏱ 6 min read
Viruses and malware have become increasingly sophisticated. Here are the key warning signs that your computer may be infected — and what to do about it.

Viruses, malware, adware, and spyware are all forms of malicious software designed to cause harm, steal data, or generate money for cybercriminals. Over 25 years in computer repair across Okehampton and Devon, Darren has removed thousands of infections. Here's how to spot them.

12 signs your computer may be infected

1. Your computer is suddenly much slower

Malware runs constantly in the background, consuming CPU power and RAM. If your previously fast computer has suddenly become sluggish for no obvious reason, malware is a strong suspect.

2. Pop-up adverts appear constantly

If you're seeing pop-up windows, browser redirects, or adverts appearing even when you're not browsing the web — adware has almost certainly been installed on your system. Some pop-ups mimic Windows security warnings to frighten you into calling fake tech support numbers.

⚠️ ImportantNever call a phone number shown in a pop-up warning. Microsoft, BT, and HMRC do not contact you through browser pop-ups. These are always scams.

3. Your browser homepage has changed

If your browser now opens to a different homepage that you didn't choose, or your default search engine has changed, a browser hijacker has been installed alongside some other software.

4. Unknown programmes appear in your system

Check your installed programmes list (Settings → Apps). If you see software you don't recognise and never installed, it may have been bundled with something else or installed by malware.

5. Your security software has been disabled

Some viruses specifically target and disable Windows Defender or other antivirus software to prevent removal. If your security software suddenly stops working or can't be opened, this is a serious red flag.

6. The computer runs hot and the fan is constantly loud

Cryptocurrency mining malware — sometimes called "cryptojacking" — runs your processor at full capacity to mine cryptocurrency for criminals. This causes constant high temperatures, loud fan noise, and extreme slowness.

7. You're locked out of files (ransomware)

Ransomware encrypts all your files and demands payment in cryptocurrency to get them back. If your files suddenly have strange extensions or you see a ransom demand on screen, disconnect from the internet immediately and seek professional help. Do not pay the ransom.

8. Your contacts are receiving emails or messages you didn't send

If friends or colleagues are asking about emails or social media messages you didn't send, your accounts may have been compromised by malware that steals login credentials.

9. Frequent crashes and Blue Screens of Death

While Blue Screens can have hardware causes, some malware deliberately causes system instability. If crashes started suddenly, malware should be on the list of suspects.

10. Unexplained network activity

If your broadband light is blinking constantly even when you're not using the internet, malware may be sending data or receiving instructions from a remote server.

11. Your webcam light turns on unexpectedly

Some sophisticated malware — known as Remote Access Trojans (RATs) — can activate your webcam without your knowledge. If the camera indicator light turns on when you haven't opened any camera app, this is extremely serious.

12. Antivirus reports a threat but can't remove it

Some advanced malware is designed to resist removal and embeds itself deeply into the operating system. If your antivirus detects something but can't clean it, you need a professional removal.

Think you have a virus?

Darren provides professional virus and malware removal across Okehampton and Devon. Full system scan, complete removal, and anti-virus setup included. Most jobs done same-day.

📞 Call 07564 432851

What to do if you think your computer is infected

First, disconnect from the internet to stop any data being sent out. Then run a full scan with Windows Defender. If the scan finds threats but can't remove them — or if you're not confident — bring it to a professional. Attempting to remove some malware incorrectly can cause more damage.

Darren at Laptop Repairs Okehampton provides full malware removal services, restoring your computer to a clean, safe state, and installing proper security software to prevent future infections.

Need a Repair in Okehampton?

Free diagnosis, No Fix No Fee, open 7 days including evenings and Sundays. Call Darren for honest expert advice.

📞 Call 07564 432851 📋 Book Online
← Blog 📞 Call Darren