Under the terms of the Senate bill, sponsored by Senators Conrad Burns (R-Montana) and Ron Wyden (D-Oregon), senders of unsolicited commercial e-mail are prohibited from using a false return address, or a misleading subject line.

Such e-mails must contain a valid way for those who receive them to 'opt out' of the mailing list, and must also contain the sender's physical address, as well as a clear indication that the message contains advertising material.

In addition, spammers will now be explicitly prevented by law from harvesting addresses from web sites, and from hacking into computers to disguise the actual origin of unsolicited e-mails.

The bill also authorises the Federal Trade Commission (FTC) to establish a 'Do Not Spam' registry, similar to the 'Do Not Call' list recently established for US citizens wishing to prevent telemarketing calls.

The federal legislation, once signed into law by the President, will supersede 35 existing state anti-spam laws.

Speaking prior to the voice vote in the House, Sen. Charles Schumer (D-New York) asked:

"Will we go after every spammer, somebody who makes a mistake here and there? No. But the studies show us - this is what gives all of us such hope - that maybe 250 spammers send out 90% of the e-mail. And we are saying to those 250, no matter where you are, or how you try to hide your spam, we will find you. This bill gives the FTC and the Justice Department the tools to go after you."

Meanwhile, in a statement following its approval, House Energy and Commerce Committee chairman, Rep. Bill Tauzin (R-Louisiana) welcomed the passage of the bill, observing that: "For the first time during the internet era, American consumers will have the ability to say no to spam."