Open Task Manager (CTRL-SHIFT-ESC) and see if mshta.exe or wscript.exe are running. If they are, congratulations: you're a moron. Kill the processes.
After that, hit Windows key + R and type msconfig. Click the 'Startup' tab and uncheck [whatever].js. It might be called run.js, or it might have a clever name like sysconfig.js or win32.js. Either way, this IS the spam script and not a vital operating system component.
After that, you should be spam-free.