In 2001 users began to receive an email informing them about an alleged
method to prevent email-aware worms from spreading by creating an address book
entry called "!0000" (some variants of the chainletter suggest other entries).
The email suggests that if the address book entry is an invalid email address
the worm will fail to spread.
Sophos advises that there are many email-aware viruses which will not be
prevented from spreading by using this technique and there is a danger that it
will lead to a false sense of security inside your organisation.