By 2003, MicroPatent had become so frustrated with its unknown stalker that it reached out to the F.B.I. for help. But with its resources spread thin, the F.B.I. could not pin down the stalkers identity, his motivations or how he managed to trespass on MicroPatents electronic turf. A year later, MicroPatent hired Stroz Friedburg and secured the services of Eric D. Shaw, a clinical psychologist who had once profiled terrorists and foreign potentates for the C.I.A.

The first order of business, investigators said, was to narrow the field of MicroPatents potential stalkers and to try to isolate the perpetrator. You need to take the temperature of the person on the other side and determine how seriously you need to take them, said Beryl Howell, who supervised the MicroPatent investigation for Stroz Friedburg. Is it a youngster or is it someone whos angry? Is it someone whos fooling around or someone whos much more serious?

Investigators said their examination of the stalkers communications indicated that he was much more than a hacker on a joy ride. That would be consistent with what law enforcement authorities and computer security specialists describe as the recent evolution of computer crime: from an unstructured digital underground of adolescent hackers and script-kiddies to what Mr. Bednarski describes in his study as information merchants representing a structured threat that comes from profit-oriented and highly secretive professionals.

STEALING and selling data has become so lucrative, analysts say, that corporate espionage, identity theft and software piracy have mushroomed as profit centers for criminal groups. Analysts say cyberextortion is the newest addition to the digital Mafias bag of tricks.

Generally speaking, its pretty clear its on the upswing, but its hard to gauge how big of an upswing because in a lot of cases it seems companies are paying the money, said Robert Richardson, editorial director of the Computer Security Institute, an organization in San Francisco that trains computer security professionals. Theres definitely a group of virus writers and hackers in Russia and in the Eastern European bloc that the Russian mob has tapped into.

Mr. Richardson is a co-author of an annual computer-security study that his organization publishes with the F.B.I. The latest version said that while corporate and institutional computer break-ins increased slightly last year from 2003, average financial losses stemming from those intrusions decreased substantially in all but two categories: unauthorized access to data and theft of proprietary information.

Among 639 of the surveys respondents, the average loss from unauthorized data access grew to $303,234 in 2004 from $51,545 in 2003; average losses from information theft rose to $355,552 from $168,529. The respondents suffered total losses in the two categories of about $62 million last year. While many cyberextortionists and cyberstalkers may be members of overseas crime groups, several recent prosecutions suggest that they can also be operating solo and hail from much less exotic climes like the office building just down the street.