MyDoom is back with a new variation that downloads a particularly nasty Trojan. This variation, also known as MyDoom.Q@mm, Worm_Ratos.A, and I-worm.Win32.Ratos, was discovered on August 15th, and jumped to a medium-level threat very quickly. While MyDoom.S doesn’t really do much, it downloads a particulary nasty trojan called Backdoor.Ratos.A.