New/recent virus outbreak

Have anyone seen any virus infected emails coming from addresses with
usernames identical to those on your own email servers, but from domains
like hotmail.com or netzero.com ? These emails seem to be sent from a
spoofed email address such as [email protected], and are sent to
[email protected]. 

Also, the attached files are always zip files, and have been named
4.zip, 5.zip, 6.zip, and work.zip .

A bounce message from one of our customers suggests they blocked an
email from on of our users that was infected with trojan.tooso.F, but
the emails stopped don't exhibit those characteristics, And even
Symantec's write-up says this virus doesn't send it's own emails.

Is it possible there's a beagle variant that is spreading the Tooso
trojan as part of it's payload? Thanks in advance.

Dan Denton
Information Technology Manager, CCNA
Pay-LESS Office Products