"unrepairable virus detected" says MAILER DAEMON....victim of spoofing?

Question

Arg. A few months ago my friend's email was put onto a blocklist, because it was detected that his mac was vulnerable to hackers. We went to a website where we requested his IP be removed from this blocklist, and everything started working as normal again. Well, today he received an email stating that an email (which he never sent) is being returned to him because the mailer daemon has detected an "unrepairable virus".....is this cause for major concern?!
Could he in fact have a virus? He uses an iMac 20"/1.8 Ghz (running on Panther) and purchased in March '05....could this make him more vulnerable than those of us running on Tiger with newer machines?
Is there any way to stop hackers from using his email address?
Will his IP eventually get block listed again?
Or is the mailer daemon email ITSELF A SPOOF?
aaaaaaaaaahhhhhhhhh
iMac G5 Intel Core 2 Duo 2.16 Ghz   Mac OS X (10.4.8)   *peace can happen*
iMac G5 Intel Core 2 Duo 2.16 Ghz   Mac OS X (10.4.8)  
Powermac G4 733 MHz, 512 MB   Mac OS X (10.3.9)  

Answer 1

Stanley,
Since wireless networking involves broadcasting traffic that can be intercepted by any appropriately tuned receiver within radio line of sight, I stand by my statement.
Second, you are creating a single point-of-failure for your network's security. Given the huge number of known router vulnerabilities, using the BSD-standard firewall ipfw, for which Apple has so kindly provided a user-friendly and easily-understood GUI, makes for a solid second layer of defense.
Making regular data backups and properly configuring your router are both VERY GOOD IDEAS(TM), but, even taken together, they are not "all the average person needs" with respect to computer security.
Computer security is a process. You have named two good practices in that process, but there is no single "magic" bullet that makes computers secure, not even for the average person.
-Wayne