I just read about a tip against e-mail worms that send themselves to your entire address book - adding an address book entry named 000 with a non-existing e-mail address. It's supposed to let you know if there's a worm at work since the worm tries to send an e-mail to a non-existing address, which causes an error message to be sent to your mailbox.
It was also said to stop the worm entirely, since the non-existing address would be the first in your address list, the worm would try sending an e-mail to that address and would stop when it fails to do so. I don't know about the first part, but this part doesn't sound very true to me