When cybercrime crusaders this week persuaded Internet service providers to disconnect a shadowy Web hosting operation called McColo, the impact was dramatic — an instant 40 percent drop in spam and other “badness'” across some e-mail networks, security experts say.

McColo, which operated from servers in San Jose, was alleged to be a conduit for activities that included fraud and child pornography, according to a “Cyber Crime USA” report issued Tuesday by an alliance of private-sector Internet security advocates.

But bringing the people behind McColo to justice, these experts say, may prove much more difficult in an age when the technology has outpaced the reach of the law — particularly when the culprits may be crime syndicates in Eastern Europe. The activities hosted by McColo were disrupted, experts say, but may be quickly revived over the Web.

HostExploit.com, a year-old alliance of Internet security entities that researches cybercrime and promotes self-policing of the Internet industry, singled out McColo as a grievous example of a company that specializes in hosting a wide range of illegal and dubious activities. Silicon Valley Internet security companies Trend Micro and McAfee contributed to HostExploit’s report.

McColo’s Web site, now apparently shut down, presented itself as a legitimate enterprise. It claimed offices in Delaware and servers operating in downtown San Jose’s Market Post Tower. Such companies as Cisco Systems and Hewlett-Packard were listed among “our partners.”

Calls and faxes Wednesday to McColo’s contact numbers found via the HostExploit report and other sources were not returned.

Hurricane Electric, a Fremont-based Internet service provider (ISP), on Tuesday unplugged McColo’s service after being shown evidence of its role in dubious and illegal activities by a Washington Post reporter. The company said it swiftly judged McColo to be in violation of its contract.

“We definitely don’t want something like that on our network,” said Benny Ng, director of infrastructure at Hurricane Electric. “I’d rather have my existing clients happy than have one who is dirtying the water.”

Another ISP, Global Crossing, disconnected McColo on Wednesday morning.

Following the shutdown, Trend Micro found a 40 percent drop in spam on its filters to corporate clients, said Paul Ferguson, an advanced threats researcher for the Cupertino company.

Enlisting ISPs in the battle against cybercrime has been a goal of HostExploit.com, said Ferguson, who contributed to the HostExploit report. “It’s not a posse. It’s a community effort,” he said.

McColo is among a small group of “bad actor” companies that charge high fees and turn a blind eye to illicit activities. They also facilitate about half the world’s e-mail spam through robotic software known as “botnets.” Much of the fraudulent activity can be traced to crime syndicates in Eastern Europe, Ferguson said.

Ferguson said he and other security researchers frequently cooperate with the FBI cybercrime squads as well as the Department of Homeland Security.

“We work closely with law enforcement. Having said that, there are difficulties in building proper cases and bringing indictments against persons unknown who may be outside the U.S.,” Ferguson said. “There is a point where the community has to take action, instead of waiting for the new sheriff to come in.”

FBI spokesman Joseph Schadler said the agency doesn’t comment on ongoing investigations, but acknowledged difficulties in combatting cybercrime.

“We are not the first line of defense against this,” Schadler said. “For so many things, your first line of defense is your corporate security. Resourcewise, we can’t be in the business of prevention. We have to be in the business of prosecution.”

Contact Scott Duke Harris at sdharris@mercurynews.com or (408) 920-2704.