"They are doing it because it's in their interest to do it," Jackman said. Spammers "are eating up bandwidth."
Jeffrey Sullivan, director of Verizon Communications Inc.'s Internet operations, said his company will not cut off a machine's Internet access until it has contacted the account owner. He said Verizon participated in the group's deliberations but is not a member.
The group, which also includes Comcast Corp. and British Telecom, said the industry should standardize several other practices, including making sure that spammers cannot automatically register for e-mail accounts without verifying their identities.
In addition, the group said, ISPs should not have servers -- computers that process mail -- that allow third parties to relay e-mail through them without being verified as legitimate account holders.
But the group was not yet ready with unified standards for verifying the identity of e-mail senders, which is one of the industry's biggest initiatives.
The four largest ISPs have been testing systems for authenticating senders to make it more difficult for spammers to disguise their identities and locations.
The companies are working with Internet organizations that help develop technical specifications, and the process is likely to take until the end of the year.
In the meantime, the group urges ISPs to prevent people from sending mail until they have been deemed valid account holders. Usually, the report said, this can be done by requiring user names and passwords to be provided before users are allowed onto e-mail systems.
Anti-spam groups that have often been critical of ISPs for not being aggressive enough said the recommendations were hardly surprising.
"It's a codification of existing best practices rather than anything that's truly new," said John Mozena, executive director of the Coalition Against Unsolicited Commercial Email.
He said that while unplugging zombies is important, the system still depends on voluntary compliance.
Mozena's group and others have sought legislation to allow consumers to hold network owners accountable for permitting spam.