McColo, a San Jose Web-hosting company that, according to computer security experts, serves as a U.S. staging ground for international firms that sell a variety of items, including counterfeit pharmaceuticals and child pornography, ceased operations after two Internet providers blocked Web access.

SecureWorks, an Atlanta security-services provider, estimates that McColo was responsible for 75 percent of all spam sent in the United States each day.

Global Crossing, a Bermuda company with U.S. operations in New Jersey and one of the two companies that provided Internet access to McColo, would not say why it cut off the company, but said Global Crossing’s policy prohibits “malicious activity.”

Benny Ng, director of marketing for Hurricane Electric, a Fremont, Calif., company that served as McColo’s other Internet provider, said it decided to block the host firm after reading about allegations against McColo.

“We shut them down,” Ng said. “We looked into it a bit, saw the size and scope of the problem . . . Within the hour, we had terminated all of our connections to them.”

McColo officials did not respond to several e-mails, phone calls and instant messages.

Paul Ferguson, a threat researcher with computer security firm Trend Micro, said that despite the actions by McColo’s Internet providers, U.S. authorities should have been looking into the company and its customers for a long time.

SNIP