TAMPA, Florida -- The State Department has launched a different sort of raid against al-Qaida - hacking into al-Qaida websites in Yemen.

In a rare public admission of the covert cyber war against extremists, Secretary of State Hillary Rodham Clinton says cyber experts based at the State Department hacked Yemeni tribal websites, replacing al-Qaida propaganda that bragged about killing Americans.

"Within 48 hours, our team plastered the same sites with altered versions of the ads that showed the toll al-Qaida attacks have taken on the Yemeni people," Clinton said Wednesday.

In response, "Extremists are publicly venting their frustration and asking supporters not to believe everything they read on the Internet," she said.

Clinton described the cyber effort as part of a larger, multipronged attack on terrorism that goes beyond attacks like the Navy SEAL raid that killed Osama bin Laden to include the propaganda battle, and the longer, slower campaign of diplomats working alongside special operations troops to shore up local governments and economies and train local forces.

Clinton was speaking alongside Adm. Bill McRaven, head of the US Special Operations Command, at a conference of hundreds of US and international special operations commanders - the two senior leaders sending a tacit message to their sometimes warring tribes of troops and diplomats that they have to get along.

Yemen is considered both a model and a test case of that effort. US diplomats have been working to stabilize the fledgling government of President Abed Rabbo Mansour Hadi, who replaced ousted Yemeni strongman Ali Abdullah Saleh. Saleh stepped down in February as part of a US-backed power-transfer deal brokered by Gulf Arab countries aimed at ending political unrest in the country after a yearlong uprising.

Hadi has faced the twin challenges of Saleh loyalists refusing to relinquish their government and military posts, and of al-Qaida attacks in the south, where the group has established a large safe haven from which to attack Yemeni troops.

The White House responded by issuing an executive order last week threatening sanctions against individuals who challenge Hadi's government. It also dispatched a new batch of special operations forces to train Yemen's army to help withstand al-Qaida attacks that have killed hundreds of Yemeni troops.

Yemen's al-Qaida in the Arabian Peninsula, is considered one of al-Qaida's most dangerous offshoots.

Yemen was the launching pad for three foiled al-Qaida attacks on US targets: the Christmas 2009 attempt to down an American airliner over Detroit with an underwear bomb and the sending of printer cartridges packed with explosives to Chicago-area synagogues in 2010. In the past month the CIA thwarted yet another plot by AQAP to destroy a US-bound airliner using a bomb which could have been undetectable by conventional airport scanners.

Clinton says the cyber attack was launched by an interagency group of specialists, including diplomats, special operators and intelligence analysts, housed at the State Department. Called the Center for Strategic Counterterrorism Communications, its experts patrol the Internet and social media to counter al-Qaida's attempts to recruit new followers.

"Together, they will work to pre-empt, discredit and outmaneuver extremist propaganda," Clinton said.

Offensive attacks on extremist sites are generally attributed to the Pentagon's US Cyber Command, though seldom acknowledged publicly.