San Francisco ? E-mailers, enjoy the early holiday gift: Spam volume has been cut by more than half because Internet providers pulled the plug on a Web hosting firm that was allegedly helping some of the world’s most dastardly junk e-mail gangs.

The break won’t last long. Garbage e-mail levels are already swelling again, and are expected to return to normal in a matter of days.

‘Tis the season, after all: The holidays are the busiest time of the year for spammers, and criminals are hustling to reconnect with potentially millions of virus-infected PCs that they once used to send spam – which accounts for 90 percent of the world’s e-mail.

Spam fighters scored big last week with the takedown of McColo Corp., a U.S.-based company apparently catering to bulk e-mailers. But the battle against McColo also highlights the difficulty in squashing spam-sending operations. Slapping one down means it just pops up somewhere else.

“It is always a cat-and-mouse game, and we fully expect there will be a countermove,” said Doug Bowers, senior director of anti-abuse engineering for Symantec Corp.

Companies like McColo can be difficult for law enforcement to take down. Authorities have to prove company officials knew crimes were being committed through their servers. Web hosting companies often argue that they don’t monitor how customers use their services.

In this case, security researchers amassed evidence of wrongdoing on their own and confronted McColo’s Internet providers to get the Web hosting service taken down.

McColo, which claims a Delaware mailing address and a data center in Silicon Valley, has been on security researchers’ radars for more than a year. Many spam filters blocked messages coming through McColo’s service.

The FBI declined to comment. However, it appears that spam senders used McColo’s service to send commands to large numbers of PCs they had hijacked.

Having that conduit is critical. Spammers use networks of compromised computers – known as “botnets,” or networks of robot or zombie PCs – to amass enough computing power to send millions of messages a day. The owners of those machines typically don’t know their computers are secretly being used for this purpose. But criminals need a way to communicate with these computers and a Web hosting company willing to look the other way.

McColo representatives didn’t return calls for comment from The Associated Press. McColo’s Web site was no longer working.