OS=Operating System. eg: windows version, linux version, freebsd version etc.

av=Anti Virus

The page you gave us shows the sasser worm. A relative old worm and if you still get infected with it then the real problem is that you did/do not kept/keep your system up to date. MS (MicroSoft) has released a patch for it even before the sasser worm was released.

I suggest you click on the link in my signature and follow all steps on that page.