Your computer is slow, something looks different, or a warning appeared. Is it a virus? Often it is not, but sometimes it is. These signs help you tell the difference.
Signs that point to malware
- New things you did not install: a toolbar, a browser extension, a new start page or search engine, or programs that start by themselves.
- Pop-ups outside the browser: ads or warnings that appear even when no browser is open.
- Your contacts receive messages you never sent: emails, WhatsApp or social media messages in your name.
- Your security software is turned off: and you cannot turn it back on.
- Files you cannot open any more: with strange new file endings and a message asking for payment. This is ransomware.
- Unknown sign-ins: emails about logins or password changes you did not make.
Signs that usually are not a virus
- A slow computer on its own: more often a full disk, too many programs at startup or simply an older device.
- Warnings in the browser that tell you to call a number: almost always a fake page, not a real infection. More in our article on fake virus warnings.
- Messages that your "subscription has expired": usually advertising that pretends to come from an antivirus company.
How to check with built-in tools
- Windows: open Windows Security, choose Virus & threat protection and run a full scan. If something is found but keeps coming back, run the Microsoft Defender Offline scan, which checks the computer before Windows starts.
- Mac: macOS has built-in protection. Check System Settings > General > Login Items for programs you do not know, and remove browser extensions you did not add.
- iPhone: check Settings > General > VPN & Device Management for profiles you do not know.
- Android: check the list of apps for unknown ones, especially those with access to notifications or accessibility.
- Every browser: remove extensions you do not know and reset the start page.
What to do if you think you are infected
- Do not enter any passwords on the affected device.
- If something is clearly wrong, e.g. files are encrypted, disconnect it from the internet.
- From another, clean device, change the passwords of your email and other important accounts and turn on two-factor sign-in.
- Do not pay any ransom and do not call numbers from warnings.
- Get help: we check the device, save your data first and remove the cause, remotely or on site.
A good backup is the best protection: if the worst happens, your files are still there.
