Huh, many years ago some Ad company asked me to write a "virus" that when the user opens some particular website, the desktop wallpaper should change after the user restarts the computer... Of course I refused, but I did implement it just for fun - some win32 app launching on system startup. The app itself was transported through ajax, and executed through Shell.Application object, all done in js. This worked in IE, including IE6. Needless to say, that code never left my PC.