Are you on a site that offers the game Allen deemed, and I quote, “Amaze-balls” at the moment? Check your address bar and if the URL is anything other than the game’s creator, stabyourself.net, you might want to close that tab. We say that because some hosts of the Portal-Super Mario Bros. mash-up, Mari0, aren’t just providing you the means to play the game. No, siree: They’d love to install some good-old malware on your computer.
The post over at the official stabyourself blog says that only one instance of the act has been discovered thus far, but it’s probably a good idea to go straight to the source for this sort of thing as it’s the best way to protect yourself.