Software that could be used to turn a Web browser into an unwitting hacker's tool has been posted to the Internet, after it was downloaded by a quick-thinking attendee at last month's Shmoocon hacker conference.

The software, called Jitko was written by Billy Hoffman, lead researcher at Spy Dynamics Inc. Hoffman demonstrated the code on March 24 as part of a presentation on the dangers of JavaScript malware.

Hoffman had discovered a way to write a Web vulnerability scanner in JavaScript, a Web language that can run in any browser. This technique circumvents JavaScript's security restrictions and, concerned that his Jitko code could be misused, Hoffman says he took extra steps to prevent the code from getting out.

However, in order for his demonstration to work, he had to post the Jitko code somewhere on the Internet. "Very briefly you could see the original URL of where the Jitko code got fetched," Hoffman said.

That was enough for show attendee Mike Schroll to snag a copy.

"I was sitting pretty close to the front and had my laptop out already," said Schroll, an information security consultant with Security Management Partners, Inc. "The second I saw it i just started typing away."

Schroll posted the code to his Web site March 25, and submitted a link to the code on Digg.com. He removed the software several hours later at Hoffman's request.

Schroll said he posted the code because he thought it would be useful to other security professionals looking for ways to illustrate just how dangerous a scripting attack can be. "I was pretty interested in it because we do some engagements with clients where we do fake phishing sites," he said. "I wasn't trying to be nefarious or malicious."

The software was downloaded from his Web site about 100 times, Schroll said.

Over the past weekend, the code surfaced again, this time on the Sla.ckers.org online discussion forum.

With Jitko now public, security researchers worry it could be misused by criminals to scan internal networks for sensitive information, or to build a malicious botnet code. "This particular tool is designed to take control of the Web browser," said Jeremiah Grossman, chief technology officer with WhiteHat Security Inc. "It will crawl other Web sites and scan them, looking for vulnerabilities."

The IDG News Service is a Network World affiliate.