php mail() genarated spam

["Νίκος Καζαντζάκης" <kazantzakisnikos () gmail com>]

hi list,

I am the administrator of a shared hosting server (linux, apache, php)
with more than 500 clients and lately we get complaints that our
server generates spam messages. Since the server is not an open relay
spam messages are probably generated from contact forms or other
similar php scripts that our clients upload to the server.

My questions:

1. Is there any tool for scanning our server and find all these forms/scripts?
2. Is there any way to log the usage of this function ?
3. Any other recomendation on this issue?

Thanks...