A tidal wave of annoying ads that shouldn’t be there washes over your screen. Unexpected pop-up ads are a typical sign of a malware infection. They’re especially associated with a form of malware known as adware. What’s more, pop-ups usually come packaged with other hidden malware threats. So if you see something akin to “CONGRATULATIONS, YOU’VE WON A FREE PSYCHIC READING!” in a pop-up, don’t click on it. Whatever free prize the ad promises, it will cost you plenty.