As a former military and Special Investigator with the OPM, I have to assume that my SSAN and other data was hacked. So, what do I do??
Right now? Put a lock on your credit (or a freeze, may cost up to $10 depending on the company - Experian, TransUnion, Equifax - do all three, just one won't cover it). If you need credit, they give you a pin to unfreeze it temporarily, then freeze it again - usually with no, or a smaller, fee. Monitor the hell out of your current accounts - try getting new cards/card numbers issued. Prevention is better than detection, Lifelock is detection, credit freeze is prevention.
You may yet receive a letter from OPM.