Whitelisting is getting a second look by some enterprises worried that unknown threats might get past antivirus and other blacklisting systems. Whitelisting, the process of spelling out exactly which applications can run on a client machine, traces its roots to the mainframe and is typically considered overkill in today’s networks, as well as a potential management headache. But the rise in zero-day attacks and paranoia about users running whatever they want on their machines (think peer-to-peer apps), or introducing malware via USB sticks, has led some organizations to think retro.