Unite was just introduced as part of the Opera 10 beta this month, but it's only a matter of time until the criminals start playing with it, according to Don Jackson, a researcher with SecureWorks. "Bad guys always need Web servers," he said. "Anything that runs a Web server is prone to attack."

But because Opera Unite runs on the desktop, it may be easier to hack than most Web servers. "In this case it's a little worse, because instead of a machine that's managed in a data center, you may have someone on a machine in a hotel network that has no firewall on it," Jackson said.

Opera attack code is already included in the majority of browser attack tools that Jackson has studied. With Unite, he expects the hackers who write browser attack software to pay even more attention to Opera. "I think there will be a push to keep your exploit kit in marketable condition by developing exploits for Opera 10," he said.

Opera says it will monitor sites for malicious or inappropriate content, but Jackson says it will prove extremely difficult to police content that's being served by smart hackers. They may, for example, send Opera sanitized versions of their Web pages and reserve the malicious stuff for all other visitors.

Botmasters might start using Unite as a platform for saving data, or for running the command-and-control servers that are the brains of their networks of hacked computers, Jackson said.