Home computer users who unwittingly send out spam e-mail should be disconnected from the Internet until their machines are fixed, the U.S. Federal Trade Commission said on Tuesday.
The FTC said it would ask 3,000 Internet providers around the globe to make sure that their customers' computers haven't been hijacked by spammers who want to cover their tracks and pass bandwidth costs on to others.
Online viruses like "SoBig" turn infected computers into spam-spewing "zombies" that send out millions of unwanted messages without the owner's knowledge. Zombie networks are responsible for 50 percent to 80 percent of all spam, according to various estimates.
Because many home users lack the technical smarts to fight the problem on their own, the FTC hopes their Internet providers will help, although they are not required to do so.
Internet providers should identify computers on their networks that are sending out large amounts of e-mail and quarantine them if they are found to be zombies, the FTC said. They should also help customers clean their machines and tell them how to keep them safe in the first place, the FTC said.
The FTC said Internet providers should route all customer e-mail through their own servers, which could upset more technically proficient users who run their own e-mail servers.
The FTC also said it plans to identify specific zombie computers and notify their Internet providers.
Law enforcers in 25 other countries, from Bulgaria to Peru, are also participating in the campaign, the FTC said.
Absent from the list of cooperating countries was China, where experts say rapid growth and a relative lack of technical sophistication have led to a large number of zombie computers.
Most U.S. Internet providers already have taken the steps outlined in the FTC's letter but they must take care not to squelch legitimate mail in the process, said Dave McClure, president of the U.S. Internet Industry Association.
"It's sometimes very difficult to tell the difference between spam coming across your network and your local charitable organization sending out its monthly newsletter," said McClure, who added that U.S. law prevents Internet providers from reading customer e-mail.
The FTC's campaign follows on earlier efforts to shut down "open relays" and other poorly configured computers that have been exploited by spammers.