What a virus actually is
A computer virus is a piece of software designed to spread from file to file or machine to machine, usually attaching itself to a program or document and activating when that file is opened or run. Once active, it can corrupt files, slow the system down, or open the door for further damage. It's called a "virus" specifically because of that self-replicating behavior — it's built to spread.
The other types of malware you'll hear about
- Spyware quietly monitors activity — keystrokes, browsing habits, sometimes login credentials — and sends that information elsewhere without your knowledge.
- Ransomware locks or encrypts your files and demands payment to restore access.
- Adware floods your browser or desktop with unwanted ads and pop-ups, often bundled in with free software downloads.
- Trojans disguise themselves as legitimate programs to trick you into installing them, then open a backdoor for other malware once they're in.
In everyday conversation, "virus" often just means "any of the above." That's fine for casual use, but it matters for a technician trying to figure out what's actually on your machine and how to remove it safely.
How infections usually happen
Most infections trace back to a small handful of causes: opening an email attachment from an unfamiliar or spoofed sender, downloading software from an untrustworthy source, clicking a link in a pop-up or ad, or running an outdated operating system or browser with unpatched security holes. Malware rarely "just appears" — there's almost always an entry point, even if it isn't obvious in hindsight.
Signs your PC might be infected
- The computer is noticeably slower than usual, especially right after startup
- Pop-ups appear even when you're not browsing
- Programs you don't remember installing show up in your app list
- Your browser's homepage, search engine, or new tab page changed on its own
- Files are missing, renamed, or suddenly show as encrypted
- Your antivirus software is disabled and you didn't turn it off
What to do about it
A few habits go a long way: keep your operating system and browser updated, be skeptical of unexpected attachments and links even from people you know (their account may be compromised), avoid downloading software from unofficial sources, and keep a real-time antivirus tool running rather than relying on occasional manual scans. If you're already seeing symptoms, the safest move is to stop using the machine for anything sensitive — banking, email, passwords — until it's been checked.