It is a common practice to append the "antivirus footers" to emails, e.g.:
Scanned by ClamAV
This email has been scanned by the XYZ Email Security service
There is many opinions about it, some say that it allows potential attacker to choose the way of attack which will avoid/bypass the revealed security mechanism.
The others say it works like a sign "Be aware, we care about our security" which could scare potential intruders.
I would like to collect all pros and cons of both approaches, I believe this kind of topic hasn't been discussed yet.