Atta surfaced thirteen different times
From the New York Post:
An active-duty military intelligence analyst has told congressional investigators that 9/11 pilot Mohamed Atta surfaced 13 times in a controversial Pentagon computer program before he executed the attacks, The Post has learned.
Congressional sources said last night that an officer in the Pentagon's secretive Land Information Warfare Center told the staff of Rep. Curt Weldon (R-Pa.) about the computer hits.
The revelation is significant because the 9/11 commission has asserted that Atta was not on the intelligence community's radar screen before the attacks.
The commission had also dismissed assertions from Weldon and others that a program known as Able Danger had linked Atta to a Brooklyn cell and included his photo on a chart of al Qaeda suspects.