At my work they use Norton Antivirus Corporate Edition version 10 on thousands of PCs without expiration date. I got it also for free. The bad thing is Windows Firewall doesn't recognize it, so I had to disable. Not bad but I don't think it's right that windows doesnt recognize it. I also have Norton Antivirus (non corporate) installed in my other pcs. I know some people doesn't like Norton but I have no problem, at least until now.
Have tried McAfee but don't like it.