The vast resources of the Internet also make it easier to cook up a story. ''Medical information is so readily available,'' Dr. Feldman said. ''You can type the most esoteric ailment into a search engine and get back dozens of pages dealing with it.''

It is, of course, easier to fool people who cannot see you or hear your voice: there is no need to shave your head or lose 50 pounds. ''These patients have often injected themselves with bacteria,'' Dr. Feldman said. ''Here, one can sit in one's bathrobe and not have to engage in those grisly things and reap the same benefits.''

The proliferation of newsgroups and chat rooms also offers a seemingly limitless audience for tales of woe. Instead of wandering from hospital to hospital, people can click from one support group to another. Some, pretending to be ill, have joined more than one, and some sign onto a single group more than once, using different names and acting out different roles.

In one case brought to Dr. Feldman's attention, a 23-year-old woman said she had an eating disorder and an abusive boyfriend she was hiding from and told people in a chat room that she was communicating with them via laptop from an intensive care unit. At times she claimed to be in shock and typed garbled messages that alarmed visitors to the chat room, who became quite concerned about her. One night she went so far as to have a stroke on line. Her mother took over the laptop and issued progress reports, but then she, too, had to be admitted to the hospital. Sometimes the father went on line as well.

The devil was in the details, and regulars in the chat room eventually began to realize that too much of the story did not make sense. All the characters misspelled the same words in the same way, and a call to the hospital where the mother and daughter had supposedly been admitted revealed that the intensive care unit was not equipped for patients to plug in laptops.

Chased out of the eating-disorder chat room, the woman turned up in others, including one for sexual-abuse survivors. She was found out and banished from that one, too, then joined another group. When last heard from, she was dying of AIDS. ''I don't need to tell you how much pain this causes others who believe her,'' one of the people who had been deceived wrote to Dr. Feldman.

In the case of the monk with cancer, Dr. Feldman said, people in his support group began to wonder how somebody who was supposed to be so sick could find the energy to send so many messages. Also, he seemed to be hanging on an awfully long time for a man with a lethal illness. When a member finally confronted him in a personal E-mail message, he confessed that he was neither a monk nor a cancer patient. He withdrew from the group and vanished, though he may well have surfaced elsewhere with a new user name and a new set of symptoms.