How can this be a virus?

I run my virus scanner (ClamXav) once a week on my iMac, and have been doing so for years as part of my normal maintenance routine. This week, for the first time I had a hit! The virus is called ‘Win.Trojan. Skintrim-5564’ and ClamXav says that this file has been successfully quarantined. My concern is that the virus is apparently in file ‘hl2.exe’, which is the Half-Life 2 game. I installed this from Steam years ago and haven’t played it for well over a year, so how could it be a virus? Malcolm Jackson-Stevens It isn’t. Win.Trojan.Skintrim-5564 is, as its name suggests, a Windows trojan. Trojans are rogue programs that attempt to trick you into running them by pretending to be something else. But you can’t run this one even if you wanted to because it’s a Windows .exe file that won’t run on OS X. It’s probably in your Half-Life 2 folder because you converted a Steam install from Windows to OS X some time ago. And to cap it all, I don’t think it’s even a trojan. Like all virus scanners, ClamXav produces some false positives. The tiny amount of OS X malware out there makes misidentifications way more likely than a true reading, and as scanners are updated with more and more Windows virus signatures, that chance can only rise. You can check this for yourself by uploading the file to virustotal.com to compare the results from other scanners.