LOS ANGELES — Some of the country’s most notorious street gangs have gotten Web- savvy, showcasing illegal exploits, making threats, and honoring killed and jailed members on digital turf.

Crips, Bloods, MS–13, 18th Street, and others have staked claims on various corners of cyberspace. “Web bangers” are posting potentially incriminating photos of members holding guns, messages taunting other gangs, and boasts of illegal exploits on personal Web sites and social networking sites.

“I’m just being real and I ain’t got nothing to hide,” said Kristopher “Kasper” Flowers, 30, a professed member of the 18th Street gang with facial tattoos of “18” and “666.” The main 18th Street gang Web site has a link to “Kaspers World.”

Gangs once only roamed the streets of big cities but now can be found in 2,500 American communities, according to the FBI. Police departments suddenly faced with the unwelcome arrivals are looking for help anywhere they can get it, including the gangs’ own easy-to-find Web sites.

The director of the National Gang Crime Research Center, George Knox, said he has trained hundreds of police officials in how to cull intelligence on gang membership, rivalries, territory, and lingo from these Web pages.

“In order to understand any subculture, be it Al Qaeda, witches, devil worshippers, or gangs, you have to be able to know their own language,” Mr. Knox said.

The tendency for gang members to brag about their exploits on Web pages such as the popular networking site MySpace.com has in some cases helped investigators make arrests.

Chicago police recently arrested a teenager accused of spraying his gang nickname on a church by tracing the moniker to his MySpace.com account. His online profile included his address, photo, and real name.

A Northern California judge ruled earlier this month that two teenagers charged with beating a boy into a coma could be tried as adults after prosecutors showed photographs of the two from MySpace.com. In the images, they flashed the hand signs of a local gang.

MySpace.com representatives could not be reached for comment.

Deputy Tom Ferguson of the Los Angeles County Sheriff’s Department’s gang investigation unit has identified a number of graffiti writers who posted to a public Web site photos of themselves in front of their work.

“Maybe they think we don’t look at it,” Deputy Ferguson said. “But we’re out there gleaning information on them.”

Mr. Knox said it’s important for police to learn how to read between the lines on gang Web sites and blogs. Just as time on the streets has given gang investigators the ability to read the hieroglyphics of wall graffiti, time on the Web helps them understand arcane Web clues. Gang identifiers, such as tattoos, graffiti tags, colors, and clothing often are embedded in each site.

“You can study gang blogs and, an hour or two into it, pick up on subtle word choices,” Mr. Knox said. “These are holy words to them.”

Mr. Knox and others fear gangs are using the Internet to recruit new members, who can be influenced by the secret handshakes, clothing, and slang of gang cultures.

“There may be a lot of wannabes out there,” a school resource officer for the Yonkers Police Department in New York and an expert on gang graffiti and Web sites, Kenneth Davis, said.

Mr. Flowers, a Hollywood tattoo artist who says he has sworn off violence, said he gets e-mails from wannabe gangbangers from far reaches of the Web but usually does not respond.

“If I do, I tell them to get a life and do your own thing and don’t try to be part of something else,” he said.