I was trying to unzip HijackThis to run a scan and post my logfile and it was halted because apparently it contains a virus. Isn't this unusual? Why is this happening?

Thank You,
Tony

Yes, that is unusual, but then I do not know where you downloaded it from.

Download it from here: http://www.bleepingcomputer.com/files/hijackthis.php

I just did and Kaspersky does not notify. If your AV still notifies, then it is a false positive that needs to be reported.