All of the email virus scanners I've used are aware of this sort of thing, and will have a maximum depth or maximum size for scanning within attachments. I don't think any of them try to "detect" them in any cleverer way.
"The Grugq: I’m not joking. You don’t even need to do that. You just send an e-mail which says, you can literally just say, "Run this code." Some of the anti-phishing guys I’ve worked with are just shocked at what happens. I had some friends who worked in corporate security who had to do a cleanup after they got hit with e-mails which said literally, "click on this" and they had 10 or 20 people who did. It was less than 1 percent, but it was enough. People will do it and even on a locked-down corporate PC, it doesn’t matter. If you can get an HTTP connection back out to the Web, you can then tunnel in over that."
You can't put it too deep. The scanner should stop attempting to unzip at a certain depth. Presumably, any file that has more than N depth is malicious and should get flagged, but who knows if the person that configured the scanner did id right?
I've worked with a leading commercial scanner that failed to respect the max depth parameter even when set. It would scan for days before we killed it.
