SYDNEY, Australia - An Australian man under investigation for illegal spamming sent more than 2 billion e-mails promoting Viagra in a year, an official said Wednesday.

Experts say that's a drop in the ocean compared to the number of spam e-mails sent globally each year, and the system he used probably wasn't very sophisticated.

The Australian Communications and Media Authority began investigating the man, whose identity was not immediately released, after receiving a tip-off from authorities in the Netherlands in May last year.

Danyel Molenaar, a project manager for the Dutch Independent Regulator of Post and Telecommunications, said the man had rented 35 servers for around 14,000 Australian dollars (US$10,493; euro8,256) each per month from a small Internet service provider in the Netherlands to carry out the alleged spam campaign.

"These 35 servers were used just for sending spam day-in, day-out for at least a year, probably longer," Molenaar said Wednesday. "This operation probably sent out billions and billions of e-mails."

Australia has some of the toughest laws in the world against spamming, the notoriously hard-to-stop practice of flooding as many inboxes as possible with unwanted sales messages in the hope some of the receivers will reply.

Under Australia's Spam Act of 2003, it is illegal for Australian residents to be involved in the sending of unsolicited commercial e-mails, even if they are generated from outside the country.

The Australian authority's chairwoman, Lyn Maddock, said the man had allegedly sent more than 2 billion e-mails, mostly promoting the anti-impotence drug Viagra, to Internet users around the world.

Officials from the authority, which is responsible for enforcing the Spam Act, had searched the man's home and were examining the evidence, Maddock said in a statement. The authority declined to give further details while the investigation was under way.

Peter Coroneos, the chief executive for Australia's Internet Industry Association, said he didn't know the specifics about the man's case. But he added that high-volume spammers don't usually use servers owned by commercial Internet service providers to generate their e-mails, because they are generally too easy to trace.

Instead, sophisticated spammers use parasitic software programs known as Trojan horses to hijack individual computers and use them as remote servers for sending spam. The method is virtually impossible to prosecute because spammers can take over an unsuspecting user's computer, send millions of e-mails in a few hours, and leave without a trace.

"An unprotected server on a reasonable connection can send out about half a million spam e-mails an hour," or more than a billion e-mails a day, Coroneos said.

Nevertheless, he said 2 billion e-mails was still "a significant amount of spam."

"If the average spam e-mail takes five seconds to identify and delete, you multiply that by (two) billion and that's essentially the amount of time he's costing Internet users," he said.

Penalties for spamming in Australia range from 220,000 Australian dollars (US$164,765) per day for first-time corporate offenders to A$1.1 million (US$823,826) per day for repeat offenders.