An anti-virus program isn't guaranteed to catch a malicious program if it's a new variant of what is otherwise, a known infection. Run this tool on each of the affected computers: http://www.microsoft.com/security/scanner/en-us/default.aspx
McAfee tends to be, IMO, iffy with detecting the latest threats. I tend to have much better results with Panda Cloud AV or Avast! when it comes down to new infections.
Ocne the machines are cleaned up, double check to make sure VISS is in fact working. Use the EICAR test website to check both realtime scanning, and on-demand scanning (eg: Right click on file, and choose scan...): http://www.eicar.org/85-0-Download.html
Lastly, make sure all of your browsers are up to date. If you're browsing with an old browser like IE8 when IE10 is available for your platform, perhaps due to some compatibility issue with a business tool, then do not use that browser for browsing. Use a modern browser, like IE10/IE11, Chrome, or Firefox for browsing instead. Sites will load faster and you'll be hardened against threats a bit more. I also fully endorse removing Java if you have no use for it on your computer. Games like Minecraft and some web utilities may require the use of Java. Otherwise it's just a big security hole as it's an often neglected program as far as updates are concerned. From there, just make sure Adobe Flash is up to date, and if you use Adobe Reader, this is also up to date. Lastly, Windows updates and UAC (Any Microsoft OS newer than Windows XP) should be on and functional. Lastly, to make cleanup of systems extremely easy, never, ever log into a Windows machine and browse as an Administrator user unless you're comfortable doing so. It's much easier to clean up a user account from a virus, and takes more effort to enter in an Administrator password to install someting, than it is to completely remove a nasty infection like a rootkit.