It depends. If you're the real person, it's 99 years. If it's a false positive, it's seven years. For a regular passenger who is cleared, it's seven days. But even seven days, in the computer age, is a long time. Before TSA erases your file, it can be copied by the 16 other agencies that are part of the Homeland Security system.
On November 25th, 2010. See this statement in context.