ISPs BT and Thus didn't respond to requests for comment on this issue.
Anti-spam company MessageLabs confirmed Linford's findings.
"This ups the ante in the need for filters," said Mark Sunner, chief technology officer for MessageLabs. "It makes it more difficult for people who compile black lists, which is why spammers are doing this. It will put more pressure on ISPs to take greater interest in the traffic they carry and filter at source."
The Information Commissioner's Office, the UK's point of call to report about spam, said it had received no complaints of bulk spam from ISPs. A statement from the ICO said, "As you are aware the ICO's role is to enforce the regulations (the Privacy and Electronic Communications Regulations 2003). If it receives complaints regarding spam, the ICO needs to establish the source of the spam to take action. The ICO then contacts the company concerned."
