The ancients got it wrong. Necessity is not the mother of invention: Pornography is.

That's the impression one might get from the Federal Trade Commission, which yesterday described two innovative scams used by purveyors of Internet smut, "page-jacking" and "mouse-trapping," to trick people into visiting their Web sites and then hold them there.

The new form of high-tech chicanery "may be the most pernicious we've seen," said Jodie Bernstein, director of the FTC's Bureau of Consumer Protection.

The two-part scheme took advantage of the tools that all Web surfers use to find things online. Scammers in Portugal and Australia copied about 25 million legitimate Web pages created by others into their own computers. Then they wrote fraudulent "meta tags"--hidden descriptions of the Web page that search engines such as AltaVista and Infoseek use to direct Internet users to those pages.

That's the "page-jacking" part of the fraud: Web surfers looking for sites describing, say, "Saving Private Ryan" or infant car seats would be initially directed to the copies of legitimate sites. But only for a moment, because extra software written into the cloned Web pages would then automatically take the visitor to adult Web sites with obviously pornographic names.

Once the visitors were page-jacked, they then found themselves "mouse-trapped." That is, anything they did to try to exit from the adult sites--trying to close the browser window, clicking on the "back" button, even typing in the Internet address of another site--only opened screen after screen of online porn, requiring as many as 20 mouse clicks to finally shut down the blizzard of windows.

Since the creators of many Internet sites earn money from advertising and set rates by the number of people who visit the sites, the scam was intended to pump up the numbers, Bernstein said. Bernstein said that no consumers lost money due to page-jacking or mouse-trapping; instead, they lost time and a sense of security in searching the Internet.

The FTC got a preliminary injunction against the perpetrators of the scam in U.S. District Court for the Eastern District of Virginia based on charges that the practices are fraudulent and unfair to consumers. The commission was able to persuade Australian authorities to raid the offices of WTFRC PTY Ltd., the home of the Aussie portion of the scheme.

The FTC is also working with Portuguese authorities. The commission also got Network Solutions Inc., the company that manages the master directory of Internet sites, to withdraw the five Web addresses used in the fraud.

Victory may be evanescent; new Internet sites can be created instantly, and for less than $100. The FTC announced its crackdown--the commission's 100th action against Internet scams--at a news conference in which Bernstein also announced a new, eight-terminal "Internet Lab" for investigating high-tech fraud.

The FTC first learned of the scam from attorney John G. Fisher, who had a client whose computer gaming Web site, www.avault.com, had been cloned. The client was losing customers to the scam, which cut into the site's advertising revenue and hurt the client's chances of selling the site to another company.

Parents interested in heading off page-jacking can turn off the ability of their browser to run "Java script," programs written in the Java programming language. The procedure for doing so varies from browser to browser. But since Java is used to create everything from animated graphics to mortgage-figuring programs, disabling the feature can "diminish the power" of the Internet experience, said Paul Lueher of the FTC's Bureau of Consumer Protection. Lueher instead suggested that parents talk to children about checking the addresses of Web sites before clicking, so that they understand where they are unlikely to find information about "Oklahoma tornadoes."

Parents can also use Internet filtering software to block pornographic sites. Programs that seek out dirty words and block sites on the fly would be likely to block the sites, though the automatic software has often been faulted for blocking many innocuous sites as well. The other major form of Internet filtering relies upon large databases of forbidden sites that can be updated regularly.

CAPTION: The FTC's Jodie Bernstein calls the ruse "pernicious."