Dealing with pop-ups

Pop-ups are one of the curses of the internet. You visit a rogue site (often accidentally) and are suddenly besieged by a never-ending stream of pop-up windows that you cannot get rid of. You are often forced to reboot your computer to exit the loop they lock you into. They are the particular stock-in-trade of crooks who run sites that trade on you accidentally mistyping a website address. (For instance, you input YouTub.com instead of YouTube.com – this one’s fairly harmless, but many turn out to be malicious.) The crooks who run these sites will occasionally get domain names very similar to common Web destinations just to catch people making such common mistakes.
Actually, there is often a simpler solution than rebooting. Hit the Ctrl-Alt-Delete combination of keys and you get the option to close down just your browser, and that often solves the problem.
Firefox and Internet Explorer both come with built-in pop-up blocker, which really do work. In Firefox, 1) click on the Tools option in the menu bar; 2) click “options”; 3) click on the “Content” icon; 4) make sure the box next to 'Block Pop-up Windows' is checked. Pop-up Blocker is turned on in Internet Explorer by default. To turn it off or to turn it on again if you've already turned it off click the ‘Tools’ button, and then click ‘Pop-up Blocker’. The rest is fairly self-explanatory.
If you are the victims of pop-ups, the big question is: Did the site do something worse than bombard you with advertising? If the problem persists, even after you've closed down your browser and rebooted your computer, then it most certainly left something malicious on your computer.
On the other hand, if rebooting appears to have fixed the problem, you still can't be sure that it didn't leave something malicious on your computer. See Remove a Virus or Other Malicious Infection for suggestions of where to go from there.