In what San Jose police said is the largest locally led child porn sweep ever in Northern California, detectives served search warrants Thursday morning at 20 homes in Silicon Valley.

Operation Chickenhawk, which involved more than 165 detectives from 30 law enforcement agencies, targeted people suspected of possessing child pornography, according to law enforcement officials.

San Jose police spearheaded the effort and anticipated making at least 20 arrests, according to Sgt. Jason Dwyer. Each of the search warrants were obtained after receiving information that link suspects to the possession or distribution of child pornography.

"We're hoping to find evidence in all 20 houses and we're hoping to tie a warm body with that evidence and take that person into custody," Dwyer said.

Officials said some of the suspects were identified in online chat room stings, where detectives posed as users and shared child pornographic images with suspects. Investigators then obtained search warrants targeting IP addresses.

As of late Thursday afternoon, police had not released information on how many people were arrested or how much child pornography they had confiscated.

An arrest at a home on Morrill Avenue was the first of the day, police said. Sgt. Jason Dwyer said evidence of child porn was found inside the home.

The Silicon Valley Internet Crimes Against Children Task Force, which coordinated the sweep, used a mobile forensic lab that allows investigators to search computers or thumb drives in an effort to find child porn images. Officials said it would ordinarily take months to obtain evidence from the equipment.

"They take the evidence from the house and into the van and fire it up on the spot, right in front of the person's house," Dwyer said.

If police find images of child pornography, the person is arrested, Dwyer said.

Since January, the task force has arrested more than 40 men for possession of child porn and in the last few months has conducted other sweeps throughout the Bay Area, including operations that resulted in arrests in Marin County, Sonoma County, Monterey County, Alameda County, San Jose and Oakland.

Thursday's sweep is of similar scale to another high-profile child-pornography bust centered in the Silicon Valley, the "Orchid Club" ring uncovered by federal agents in 1996. Sixteen people were tried in federal court for participating in the real-time sexual exploitation of young Monterey County girls via the early incarnations of the Internet, with a prison guard being identified as the group's ringleader.

Those initially identified and booked on felony possession of child porn were: Yun Chen, 36, a software engineer; Tom Truong 27; Valentine Hyjek, 46, an IT tech; Lorenzo Caliva, 22; Ismael Aragon, 53; Brandon Hellewell, 18; Davide Signorelli, 30, a computer hardware engineer; and Luis Benavides, 29, all of San Jose; Robert Hernandez, 32; Tony Silva 64; and Mark Flores, 31, all of Santa Clara.

Contact Mark Gomez at 408-920-5869.