ONDON, Jan. 13 - Inside a nondescript office building here, investigators for the Business Software Alliance are working to track down software pirates around the world. To help maintain secrecy, they often rely on several computers running on different operating systems, with special programs allowing them to switch Internet service providers every 60 seconds.

"I can be perceived to be in China in one minute and in the U.S. the next minute, so they wouldn't be able to track it back to me,'' said one investigator, who allowed a reporter to follow his activity on the condition he not be identified.

Long before downloading music and movies became a hobby of teenagers and others, the software industry was struggling to keep digital pirates at bay. Even in the pre-Internet 1980's, introducing software was fraught with peril.

"If it didn't have copy protection, you lost that market, and you would never get it back," said Deanna Slocum, an antipiracy manager at Macromedia, which makes multimedia business software.

Since then, the industry has developed techniques to safeguard programs and thwart pirates, and global software piracy rates have declined somewhat. Yet the advent of peer-to-peer, or P2P, file-sharing programs like Kazaa is quickly eroding those gains. As many file-swapping advocates note, P2P is agnostic - it embraces all digital files, be they Beastie Boys songs, knitting patterns or high-end computer programs.

The amount of software piracy attributable to Internet file sharing is difficult to determine, in part because not every downloaded file represents a successful installation. But William Plante, director for worldwide security at Symantec, estimated that roughly half of the illegal copies of his company's software, which focuses mostly on protecting computers against viruses, stem from electronic downloads.

The Business Software Alliance estimated global losses from all software piracy at just over $13 billion in 2002. The global software market that year was valued at $152 billion, according to Ovum, a research and consulting firm.

"Internet piracy is the fastest-growing form of piracy," said Jeffrey Hardee, a vice president of the alliance. "It's really quite phenomenal.''

Why now? One reason is the ascendance of high-speed Internet access, which makes downloading giant files feasible for millions more people. Convenience is another: the easy use and availability of free peer-to-peer software largely makes it unnecessary to learn older and more complex file-exchange systems like FTP or Usenet.

"Increasingly we're finding that people are skipping straight to P2P," the investigator for the alliance said.

The organization, which has three antipiracy monitoring centers - one here, one in Washington and one in Singapore - is loath to have the exact locations of these operations disclosed, because its investigators are sometimes subject to threats from those who object to their antipiracy efforts.

Sitting at a computer in the center, the software investigator quickly spotted a P2P site offering multiple versions of popular (and expensive) programs like Macromedia's Dreamweaver, Adobe's GoLive and even a full version of Microsoft's Office XP. Many contain text files that explain how to install the software, which has been "cracked'' by hackers to defeat its copy protection, making the process almost foolproof.

Beyond relying on an automated Web crawler that scours the Internet for unauthorized files, alliance investigators also try to snare pirates by gradually building relationships with them, using assumed identities. After pinpointing a transgressor's Internet address, they send a note to the company that provides Internet access to the pirate, requesting that the files or sites be removed. The responsiveness varies, but service providers on good terms with the software alliance often comply "within a few hours," the investigator said.

But as some pirates find better ways to mask their identities, it is becoming harder to track them. "They're truly ghosts on the Internet now,'' Mr. Plante of Symantec said. "They're virtually untraceable."

Another problem is users' motivation. Fly-by-night Web stores that sell pirated software on CD's and DVD's are a nagging reality, but many pirates are in it for the kicks.

"It's about getting recognition," said Drew McManus, who directs Adobe's antipiracy operation. "It's about being the first or the best at cracking."

Some are so fast that pirated versions of new programs often hit the P2P networks before they are officially released, a problem that also plagues Hollywood.

Adding to the worries is the relatively recent appearance on P2P sites of high-end business software like AutoCAD, an industrial design program that can sell for more than $3,000. "You basically need to be trained in that in order to use it," the alliance investigator said. "It's a professional program."

How are the software companies fighting back? "I don't think anything is off the table," said Robert M. Kruger, a vice president of the software alliance. "You're competing against free, and that's hard to do."

One approach is mandatory online activation, which Microsoft, Adobe, Symantec, Macromedia and others, have introduced for some products. Software pirates have already cracked many of these new registration methods, a familiar development in the antipiracy battles.

"Yes, you can crack it," Mr. Plante said, but he added, "It's extremely inconvenient to try and use the cracked version."

Smaller software firms that cannot afford pricey copy protection technology sometimes adopt an ambivalent attitude toward peer-to-peer theft. Edwin de Koning, a Dutch programmer, created with a colleague, Bart van der Ploeg, a video mixing program called Resolume that sells for about $200. The program, which has attracted a few hundred buyers a year, recently began proliferating on the P2P networks.

That "hits us in the wallet directly," Mr. De Koning said. "But in the end, there's also a positive side. There's more and more video software coming out, so in the beginning we want to get a big share of that. If there weren't P2P software, I think we would be less popular."

Building a customer base in part through illegal copying is anathema to many in the industry. "I strongly take exception with someone that would promote the idea of seeding the market with illegal copies so that they could somehow get future revenue," Mr. Plante said. "That's just a flawed business model."

A more nuanced solution revolves around meeting the P2P networks halfway. In 2002, for example, Microsoft used the Kazaa network to help start its media player, which is free software for anyone who has the Windows XP operating system. "By promoting Media Player 9 through P2P networks, Microsoft is embracing the promise of P2P technology, while respecting the importance of preserving intellectual property," Tim Cranton, a Microsoft lawyer, said in an e-mail response.

Mr. McManus of Adobe says he is also intrigued by the potential of P2P. "We've actually been looking at Kazaa specifically," he said. "Adobe's always interested in innovation, and if there's ever a more efficient way for our customers to get our software, I think we have to look at it."

But Josh Bernoff, an analyst at Forrester Research, warns: "One reason not to do that is that it helps legitimize the existence of these services. It's the same argument that allows you to buy a crowbar, despite the fact that it can be used in a burglary."

The P2P proprietors say they would welcome more cooperation with the software industry. Michael Weiss, the chief executive of StreamCast Networks, which makes Morpheus, a popular P2P program, has been challenging copyright law since he opened one of the world's first video stores in 1978.

The software industry, he said, "has to embrace the technology, just like the movie studios ended up embracing VCR's." He said he would "love to engage in discussions with the companies that want to," but added that in some respects their participation was immaterial.

"This is not going to go away," he said. "Technology always wins out. You would think the software companies would know that more than Hollywood."

Software files, however, may by nature be impervious to some of the problems that beset the entertainment industry's movie and music files. "Software is not just the code that comes with it," said Ms. Slocum of Macromedia. "Software is also the technical support, the customer service, the upgrades" - extras that are largely unavailable to users of illegal versions.

Eric Garland, chief executive of BigChampagne, which monitors file swapping for the entertainment industries, said that music and video accounted for 88 percent of the files on P2P networks (the other 12 percent consists of software and "everything else.") He says he sees this moment as a chance for the software industry to flourish where the entertainment industry has floundered.

"It's the carrot, not the stick,'' Mr. Garland said. "The only way to really marginalize online piracy is to make online retail so transparent, so convenient and so appealing that when you're faced with two icons - one that's an unknown, perhaps virus-infested crack on Kazaa, and the other that's double-click to download the legitimate version" - users will naturally turn to the official version.

In the meantime, the software alliance's sleuths have plenty to keep them busy. The organization recently discovered a P2P site, whose name the investigator declined to make public, that offers verified downloads of innumerable programs and can even locate files invisible to other P2P programs. You will not find it through Google.

"It's incredible how much you can get," he said. "It's too easy."

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