Klez Worm

Whilst the Klez worm is not considered to be as destructive as other worms, what makes it worst than most is how difficult it is to detect and remove. It is also widespread and still active. In fact, to date, no other virus has stayed in circulation quite like the Klez worm. Unleashed in 2001, it blends the traits of different viruses, being distributed like a virus, sometimes acting like a worm, whilst other times like a Trojan horse.

Klez spreads via open networks and email traffic, sometimes masquerading as a worm-removal tool. Unlike many other worms, it is not tied to any particular email client. On infected machines, after grabbing email addresses from a victim's address book, it mixes and matches these addresses to create new senders and recipients aimed at spreading the infection further. The destructuve effects of the Klez worm are to corrupt files and disable anti-virus products.