If 1 in 200 messages is infected, I'd guess that 1 in 400 is a return message (I receive a lot of these). Although the mail was sent with good intentions, it demonstrates a lack of understanding of infection vectors and is basically a waste of resources. For AOL, the message size was 4K. Because it was an error message, it was sent to my account and root on my mail server, so I get to delete this twice. This also ate up 8K of bandwidth. For me, it's not that bad. For AOL, it has to be monstrous (i.e., they're wasting their own money).
If your anti-virus utility scans inbound email for viruses, please TURN OFF your auto-response feature. It actually compounds a number of problems (bandwidth, storage) rather than prompting the owner of an infected machine to fix his junk.