deadly computer viruses

With the mix characteristics of a virus, worm and a Trojan horse,?Klez?gave the antivirus programs a real headache by simply disabling them and making them look like a joke. However this is only the beginning of its trickery; after it was thought it be defeated, it was taken over, decoded and customized by black hat hackers (hackers who specialize in unauthorized penetration). Its ability was enhanced by providing it with the capability to spoof from the?users?address?book and make it look like that an email came from them, increasing the chances of the receiver opening the email and becoming the next casualty.