It looks like it's sufficient to do it with one as the alert propagates to the other two. And it lasts 90 days. "Ask 1 of the 3 credit reporting companies to p

It looks like it's sufficient to do it with one as the alert propagates to the other two. And it lasts 90 days. "Ask 1 of the 3 credit reporting companies to put a fraud alert on your credit report. They must tell the other 2 companies. An initial fraud alert can make it harder for an identity thief to open more accounts in your name. The alert lasts 90 days but you can renew it." [http://www.consumer.ftc.gov/articles/0275-place-fraud-alert http://www.consumer.ftc.gov/articles/0275-place-fraud-alert]