What can I run to detect network based malware infection?

[Spooter]

Hi all,

Im after something free to detect network-based malware infection?

Something Free?

I have found http://www.bothunter.net/ which is based on ubuntu, has any of you heard or used this before?

I trying to troubleshoot a problem where two users are showing as logged onto a couple of machine in another office but have no memory of trying to.

I have ran Viruscans/antispyware/hijackthis on the machines and found nothing unexpected.

Any ideas?