The fraud alert will remain in place for 90 days. You'll have to reactivate it yourself. Or if you're lazy like I am, some companies will do this for you for a fee. If you can prove that you've been a victim of ID theft, you can apply to keep the alert in place for 7 years.

That said, fraud alerts are only part of the solution. I have no idea why, but sometimes creditors ignore fraud alerts. So it's still a good idea to get a copy of your credit report from time to time.