Computer virus symptoms

1. Pop-up ads

Running into a pop-up ad while you're surfing used to be a serious annoyance, but modern browsers include pop-up protection to keep these annoyances away on most sties. If you're still seeing regular pop-ups on more than one site, it could just be a badly-configured browser.
However, if pop-ups are coming at you when your browser isn't even open, it's likely you have a virus. This is especially true if the pop-ups advertise some magic cure-all to your "virus woes"

2. Messages you didn't send

Most viruses have one goal in mind once they infect your computer: to spread the virus as far as possible. An easy way to do that is to send messages to as many of your friends as possible in hopes they'll get infected, too.

3. You're locked out of your computer

You're surfing the Web when suddenly a scary message appears saying you're locked out of your computer. It may claim to be from law enforcement or an anonymous blackmailer.
Either way, the program is lying. What's really happening is that a virus is blocking important programs from running, or even encrypting your files so you can't get to them. The scam is trying to make you pony up some cash to get your computer back. That's why it's commonly called "ransomware."

4. Programs and tools are out of reach

More often than not, a computer user will rely on one simple command when their computer starts misbehaving: Ctrl + Alt + Del. The "three-finger salute" opens up Task Manager, which can tell you so much about your computer.Sometimes, however, you'll hit this keyboard shortcut and nothing happens. You might get a random error message, too. This is a dead giveaway that a virus is messing with your computer. It's stopping Task Manager so you can't see that it's eating your system resources or shut it down.

5. You're not seeing any symptoms at all

No news isn't always good news when it comes to viruses. Powerful viruses can hide deep in your computer without raising any red flags. They'll just go about their business without you even knowing they're there.
Just because you don't notice them doesn't mean they aren't dangerous, though. They could be snagging your passwords, sensitive files or other vital information from your computer. The virus could be using your computer to spread to other computers or even attack banks and other organizations.