Presently their are various mail worms are spreading these worms are intelligent worms some time send mails to all of ur contact list with any of the previous mail subject line.
To avoid this following measures are very useful.
1) Create 2 mail ids in address book one with name:
( so that it wil be the 1st contact, and should not enter any email address for that)
and another with ID: **firstname.lastname@example.org*
this creates confusion to any normal virus/worms in the first try of its sending the mail itself!*
Second mail box is very handy tool for any mail server administrator because they can track easily weather their network having such virus or not . If their is mails coming on this mail box means virus/worms are their.