Terror Suspects Hone Anti-Detection Skills

"Taxi drivers," Redouane el Habab said, referred to suicide bombers; explosives were "dough." Anybody who had to go to "the hospital," he added, had been taken to jail, while those visiting "China" were really attending training camps in Sudan.

Experts said the codes may not appear sophisticated at first glance but can be time-consuming to crack, especially if the targets are conversing in Arabic.

In September 2005, a British court convicted Andrew Rowe, a Jamaican convert to Islam, on terrorism charges after authorities found a secret code book in which he gave double meanings to the brand numbers of Nokia phones.

Pretending to be a traveling cellphone salesman, Rowe would use "Nokia 3310" to refer to money, "Nokia 3410" to signal potential trouble from the police and "Nokia 3610" as code for weapons. Rowe received a 15-year prison sentence, even though prosecutors and police said his precise plans remained a mystery.

"They are very creative on this front. It is one of the most interesting dimensions in this cloak-and-dagger war on terrorism," said Magnus Ranstorp, a terrorism analyst at the Swedish National Defense College . "They are incredibly aware when they use any electronic means to communicate that they can be monitored by the intelligence services all over the world, not just Europe."

Coded language was also cracked in the FBI investigation of Jose Padilla, the Brooklyn-born al-Qaeda follower who was convicted last August of conspiracy to commit murder.

According to prosecutors, Padilla and two co-defendants were bugged for years by the FBI, which eventually concluded that their frequent mentions of "eggplant" and "zucchini" were really references to weaponry and ammunition.

In Germany, police said they were taken aback by some of the tactics employed by the three-member cell that was charged in September with plotting to bomb American targets. To communicate with operatives in Pakistani training camps, cell members rarely used the same computer more than once, sometimes driving more than 100 miles to find a new Internet cafe.

Other times, they cruised through randomly picked neighborhoods in search of unsecured wireless connections, all in an effort to make it more difficult to monitor their e-mail traffic and Web searches, police said.

The cell was traced only after U.S. intelligence officials noticed suspicious electronic communications originating in Pakistan, counterterrorism officials said. Police said they later determined that the suspects had received anti-surveillance training in Pakistan.

"It's one thing to follow the foot soldiers or the ones recruited to be suicide bombers; they're often not very smart," said Rolf Tophoven, an analyst at the Institute for Terrorism Research and Security Policy in Essen, Germany. "But it's different with the elite ones, the clever guys who are Internet experts with white-collar jobs, sitting behind a desk. They are very sophisticated professionals who are able to counter the surveillance of the intelligence agencies."

The cat-and-mouse game has evolved in recent years as technology advances.