You’re familiar with pop-up ads – the windows that appear spontaneously when you visit many web sites. Are you ready for pop-up downloads? Watch for a box to appear asking you to confirm a download, when you don’t recall asking to download anything. (Sometimes the download box is hidden in a blizzard of other pop-up ads.) If you say “yes,” you’ll automatically install some software that might be benign or might be harmful. In either case, it’s a sneaky tactic. Here’s an article with details.
Gator is the most widespread of the stealth programs, by the way. It masquerades as a legitimate product, but mostly it delivers ads and ads and more ads. If you get any hint that Gator made its way onto your computer, go to Control Panel / Add-Remove Programs and yank off Gator and its little brother, “Offer Companion.” Yucky stuff.