Three people accused of sending massive amounts of spam face possible prison sentences after being indicted by a grand jury in the U.S. state of Arizona and accused of violating the CAN-SPAM Act of 2003 and other charges, the U.S. Department of Justice said in a statement.

Named in the indictment are Jennifer R. Clason, Jeffrey A. Kilbride, and James R. Schaffer. The three are accused of sending spam that advertised pornographic Web sites, said the DOJ in a statement. They could make money from commissions that the Web sites paid in return for directing traffic to their sites, the statement said.

The defendant’s operation was ranked as one of the 200 largest sources of spam on the Internet by The Spamhaus Project Ltd., a group that tracks and battles against spam. America Online Inc. received more than 600,000 complaints between late January and early June last year related to spam from the operation, said the DOJ. The actual number of users who received spam from the operation could be in the tens of millions, it said.

“Each of those people [in the Spamhaus listing] sends out several million spams a day,” said Suresh Ramasubramanian, who heads anti-spam operations at e-mail outsourcing company Outblaze Ltd.

He said the defendants’ operation worked by buying large amounts of Internet bandwidth from major service providers. With the purchase they’d also get large blocks of IP addresses and the defendants would then send spam to the Internet from a small portion of the addresses they had. Once the addresses were blocked in anti-spam systems they’d start using different addresses until such a time as the pattern was recognized and they were terminated by their ISP. They’d then go to a new service provider and start all over again.