A former AOL employee has been sentenced to 15 months in prison for selling members' details to spammers.
The US CAN-Spam law is designed to smother unsolicited e-mail
American Jason Smathers, 25, said he turned into a "cyberspace outlaw" after selling the database of 92 million screen names and e-mail addresses.
As a result of his actions in 2003, about seven billion unsolicited spam e-mails flooded inboxes of AOL members.
Prosecutors said Mr Smathers had violated recent Can-Spam laws, which aim to clamp down on unsolicited mail.
He was also accused of breaking US interstate transportation of stolen property laws.
Mr Smathers admitted accepting $28,000 (£15,515) from an individual for the list of AOL member details. The details are still thought to be circulating amongst spammer rings.
"I know I've done something very wrong," Mr Smathers told US District Judge Alvin Hellerstein via a letter.
"Cyberspace is a new and strange place," Mr Smathers wrote. "I was good at navigating in that frontier and I became an outlaw."
Assistant US Attorney David Siegal concluded that the case had shown that the net was "not lawless" anymore.
"The public at large has an interest in making sure people respect the same values that apply in everyday life, on the internet," he said.
Mr Smathers' lawyer added that the theft had been a "dumb, stupid, insane act".
AOL said Mr Smathers' act had cost the company at least $300,000 (£166,240), although the judge said that figure was speculative.
The judge ordered Mr Smathers to pay $84,000 (£46,560) in restitution, but he delayed the order so that AOL could prove whether the damages were higher.
Mr Smathers was fired by AOL in June 2004. He was said to have used another employee's access code to steal the list of AOL customers in 2003 from its headquarters in Dulles, Virginia.
The US CAN-Spam legislation (Controlling the Assault of Non-Solicited Pornography and Marketing Act) was introduced in the US in January 2004.
The US and UK laws to control spam have been criticised as ineffective. Some legal action in the US has had to be brought against individuals or groups using local state laws instead.
Spammer Jeremy Jaynes was recently sentenced in Virginia, where there are tough anti-spam laws, to nine years in prison for sending 10 million junk e-mails daily.
But unsolicited e-mails in the US rose by 10% after the introduction of its anti-spam laws.
The majority of spam originates outside of Europe, from the Americas in particular. UK spammers account for less than two percent of all junk e-mails sent.
The anti-spam campaign group, Spamhaus, estimates that by summer 2006 spam will account for 95% of all e-mails sent. It said that spam would not stop until the US acts to toughen its laws.
Last week, software giant Microsoft has won a $7m (£3.9m) court settlement from a businessman considered to be one of the world's biggest senders of spam e-mail.
Scott Richter agreed to pay the sum after Microsoft filed a lawsuit against his net firm Opt In Real Big.
Loopholes in UK law mean legislation is ineffective in the fight against spammers, according to Spamhaus.
Since UK anti-spam laws came into force more than a year ago no UK spammers have been fined or prosecuted.