Aaron Weaver has made a discovery the world could probably do without. He's found a way to spam your printer from the internet.

By using a little-known capability found in most browsers, Weaver can make a web page launch a print job on just about any printer on a victim's network. The website could print annoying adverts on the printer and theoretically issue more dangerous commands, such as telling the printer to send a fax, format its hard drive or download new firmware.

Weaver, a Pennsylvania-based security manager in the financial industry, described what he calls "cross site printing" in a research paper published on Tuesday on the Ha.ckers.org website.

For a cross-site printing attack to work, a victim would have to visit either a malicious website or a legitimate page that suffers from a cross-site scripting flaw, which is a common type of web programming error. The hacker would then send JavaScript code to the browser that would guess the location of the victim's printer and send it a print job.

Weaver has launched the attack successfully with both the Internet Explorer and Firefox browsers. Because the attack works only on network printers, a printer plugged directly into a PC would not be vulnerable.

The attack is possible because most browsers can connect to the networking port used by most printers to look for new print jobs. So by using the browser as a stepping stone, attackers are able to connect with something they should never be able to reach: a printer on the local area network.

While nobody had previously demonstrated this particular hack, Weaver's research is based on two concepts that are well-known to web security researchers: cross-site scripting attacks and vulnerabilities in the way browsers handle the Internet Protocol. "There's no precedent for [this hack]," said Robert Hansen, CEO of web security consultancy SecTheory and owner of the Ha.ckers.org website. "But what he did was marry two different concepts we've been talking about for a long time."

And if hackers figure out a way to make printers send out information about their print jobs to the internet, Weaver's hack could have even more profound security implications, Hansen said.

Researchers have already shown how the browser can be used as a gateway to reach mail or voice over IP (VoIP) servers. They believe that the browser, with its ability to connect the internet at large to the local area network, will be an increasingly important source of network attacks. "There are definitely a lot more exploits to be found," Hansen said.

Browser developers are already aware of the problem.

The Firefox browser blocks ports known to be associated with known security vulnerabilities, but it leaves many of them open because web developers often use these ports in web testing, said Mike Schroepfer, Mozilla's vice-president of engineering. "If this is a new problem, we can easily add 9100 to the blacklist," he said. "Folks here haven't done enough analysis to understand the impact yet."

Weaver said concerns that his research might unleash a new blight on the internet caused him to hesitate before publishing his paper and hold off on publishing the complete exploit code.

By yesterday he'd already received his first request from someone asking to look at his software - someone saying he needed to show it to his manager in order to prove that it was a real issue. Weaver said he suspects the inquiry may have come from a spammer.

So will we see cross-site printer spam flying around our networks soon?

Weaver believes there's a good chance of that happening. "Spammers will try anything," he said.