Mars Attacks!

In the very early days of Windows, there was a program called Gopher, which caused gophers to dig holes into your open windows, and poke there heads up. A more sophisticated variant on the theme can be found at Netdisaster.com. You get a selection of choices allowing you to dynamically deface any web page. As in this screenshot from O-n-A getting attacked by flying saucers with energy weapons (flash required). Fortunately, they offer an auto-repair function to fix the damage.