For members of Osama bin Laden's terrorist network, a picture could really tell a thousand words — but ordinary people and law enforcement personnel might not know it.

Authorities trying to follow the cyber-trail of terrorists linked to recent attacks face a daunting task. While some e-mails between operatives in America have been recovered, bin Laden's organization also uses a full array of encryption tactics, experts say, including concealing hidden messages within the source codes of images, in order to communicate covertly over the Internet.

During a meeting in with the Senate Intelligence Committee last February, security officials reportedly said that bin Laden's associates were hiding messages in image files and chat rooms on the Internet, perhaps even within online pornography — a bizarre choice for the devout Muslims.

"They put encrypted messages within all sorts of files. Bin Laden's up on the latest technologies. The guy can do anything that any other techno-junkie is capable of," says Harvey Kushner, author of "Terrorism in America and The Future of Terrorism: Violence in the New Millennium."

Image files just consist of source code, and concealing text within that code isn't that difficult, according to Dorothy Denning, a Georgetown University computer science professor and expert on cyber-terrorism.

"It's very simple, I'm afraid," she says. "There are simple and easily available software tools for this. You select an image file. You type your covert message in another file, then combine and encrypt them with the software program. It will ask you for a password, which is the encryption key. Then somebody else with the password can uncover the message, but it won't be apparent to anybody else."

While the encryption used isn't that tough to crack, finding the files is the real problem. They don't necessarily need to be sent to other members of al-Qaeda, bin Laden's organization. Instead, they can just be posted at a prearranged location on the Internet — estimated now to have two billion pages containing 28 billion image files.

"The Internet's just too big to keep track of," says Kushner, offering an assessment not shared by some information technology professionals.

"There are ways to sift through the data. The fact that the Web is so huge isn't an insurmountable problem. The problem is that intelligence agencies need better systems," says Tim Belcher, chief technology officer for Riptech, a leading online security firm based in Virginia. "There's always going to be a see-saw effect between the good guys and the bad guys."

Complicating law enforcements' task, there are many different ways to hide communications. Denning points out that a program called "spammimic" can be easily downloaded that will disguise an e-mail message as unintelligible spam.

The e-mail can then be sent to thousands of other people, hiding the true recipient, who has a key to convert the spam back into the original message.

According to experts familiar with bin Laden's operation, the terror mastermind has used these techniques since the mid-1990s, but began relying more upon information technology a few years ago when he discovered that the CIA was listening to communications on his satellite phone.

"We were stealing his homework. We knew a lot. But when the phone stuff came out, he changed," says Edward Turzansky, a professor of political science who has held several defense positions within the federal government.

A 1998 FBI indictment says that a chief bin Laden operative recently convicted of bombing American embassies in East Africa communicated using encrypted e-mails sent under pseudonymns from a variety of accounts.

In addition to greater secrecy within terrorist cells, on-line communications also helps bin-Laden's organization remain compartmentalized. Experts say leaving messages in various nooks and crannies of the Internet is modern equivalent of the "dead drop," a technique used by spies to leave information for other operatives without having to meet them or know their identity.

But while bin Laden's use of information technology has befuddled some authorities, Turzansky says the recent attacks present law enforcement with an unprecedented opportunity to investigate known cells of the terror organization.

"Think of intelligence as a huge puzzle," he said. "We were sitting there with 1500 pieces, not knowing how to proceed. Now somebody's handed us the box with the picture on the front."