Hayden's remarks were made in a videotape statement distributed to CIA employees around the world.
Hayden called the 9/ll attacks "an unforgettable blow" from a "plot we had not been able to prevent."
Since then, he said, "Al-Qa'ida's core operational leadership has been decimated, and theirsuccessors are in hiding or on the run."
Hayden paid tribute to four CIA employees killed in Afghanistan: Mike Spann, Helge Boes, Chris Mueller and William Carlson.
Veteran CIA officers continue to praise the leadership of Gen. Hayden, who took over earlier this year from Porter Goss.
As part of his effort to highlight CIA accomplishments, his videotape statement was distributed to reporters.