sorry.
[/sarcasm]
there we go.
Well... He's maybe just being sarcastic, but the other day the strangest thing happened: I'm the monitor of the Mac room at my faculty, and I had the biggest argument with the IT guy (he's a Windows expert and knows nothing about Macs, but he handles all the PCs over there and also the network), as he insisted my Mac Pro running Leopard (10.5.8) was opening way too many ports and sending way too many packets over the network, thus crashing the firewall in the process...
I've sworn that I hadn't installed anything vaguely suspicious in months (and I really didn't, at least consciously, so if it was a trojan it was very well disguised because I'm not the kind of guy that falls easily for social engineering crap), to no avail; he temporarily blocked my machine's MAC address, until I found a solution for that issue (and reformatting the startup volume was NOT an option, as I didn't have an updated external backup anyway)... And much to my chagrin, he kept insisting that my machine must've been infected with some kind of malware, just to be met with my firm denial (am I on denial?).
That Leopard installation was still from my old Rev.A iMac G5 hard drive upgrade, partitioned under an Apple Partition Table (and not GUID, which prevented me from upgrading the boot volume to Snow Leopard without reformatting all the other volumes in the process), but fortunately I just added it alongside the Mac Pro's original hard drive which I did upgrade to Snow Leopard.
Booting from that original volume apparently fixed the problem, and everything's been fine ever since, even after I painstakingly reinstalled all my essential software (fully-legal CS5 Master Collection FTW, yay!) and transferred over my work-related stuff, personal e-mail accounts and iTunes library (hey, I absolutely need music to be a happy and productive worker

)...
I still haven't run ClamXav on that other drive (which I will eventually do, evidently unplugged from the network, if not out of sheer curiosity), but I was scared enough to install and use it at least on my home computer (funnily enough, I found a few old Office macro viruses on the process, no biggie). Maybe I did have some OS X-specific dormant malware installed on my work computer, because I really can't find another explanation for what happened... If you know of some other possible causes (could it be hardware-related? But, then again, after booting from another volume the problem was gone for good!) for such random behavior, feel free to chime in!
Sure enough and for good measure, I've also installed it and will be configuring it on the other Mac room I'm also managing, the Communication Design Master's room in which I also study now, and will do the same on the main room after our new iMacs arrive (I'm not really bothering much with a bunch of old PowerMac G5s running Leopard, though, as they haven't been giving any trouble anyway).