Seven signs your computer has a virus (and what to do about it)

Not every slow computer has a virus, and not every virus announces itself. Some malware is loud and obvious; some sits quietly and steals. Here are the signs we most often find when we're called to a computer that's been infected, plus a few that people worry about but usually aren't one.

Seven genuine warning signs

1. Popups that won't go away. Constant ads, or full-screen warnings telling you to call a number, even when your browser is closed. See That "Microsoft" popup is lying to you.
2. Your browser behaves strangely. The home page or search engine has changed by itself, you're redirected to sites you didn't ask for, or there are new toolbars or extensions you didn't install.
3. Programs you didn't install. New apps, especially "PC cleaners", "optimisers" and "security" tools, that you don't remember adding.
4. Your computer suddenly gets much slower, with the fan running hard when you aren't doing anything demanding.
5. Your friends get odd messages from you. Emails or social media messages sent from your account that you didn't write. That's usually a hacked account, which is related but not quite the same. See Your email has been hacked.
6. Files vanish, are renamed or won't open, or a message says your files are locked and demands payment. This is ransomware: switch the computer off and call for help.
7. Antivirus is switched off and won't turn back on, or has been replaced by something you didn't install.

Things that look like a virus, but usually aren't

• A slow computer on its own. An old hard drive, too little memory or too many startup programs are far more common. See Why is my computer so slow?
• Windows updates running. Heavy background activity after an update is normal for a while.
• One site behaving oddly. The problem may be the website, not your computer.

What to do if you think you're infected

1. Disconnect from the internet (turn off WiFi or unplug the cable). This can stop malware from spreading or sending your data out.
2. Don't log in to banking or email on that computer until it's been checked.
3. From a different, trusted device, change your important passwords, starting with email and banking.
4. Run a full scan with Windows Security (the built-in antivirus). It's decent, and a good first check.
5. Don't install a random "cleaner" or "remover" from a popup or search result. Many of these are the problem. See Free "PC cleaner" apps usually make slow computers worse.
6. Back up what matters if you can do it safely, and if the machine is badly affected get a professional to look at it before copying anything.

When a scan isn't enough

Some infections hide from scanners or leave behind remote access tools, browser hijacks and stolen passwords that need proper cleanup. If you've given a stranger access to your computer, or paid money after a call or popup, treat it as serious and act immediately.

Our local technicians remove viruses and malware and then check the whole computer, including accounts. See our virus and malware removal service, call 1800 851 816 or book a visit. There's no call-out fee, and No Fix No Fee.

Related guides

• "Your computer has a virus" phone call? It's a scam. Hang up.
• How to back up your computer properly