The upcoming Black Hat security conference in Las Vegas offers an annual parade of security researchers revealing new ways to break various elements of the Internet. But few of the talks have titles quite as alarming as one on this year's schedule: "How to Hack Millions of Routers."

Craig Heffner, a researcher with Maryland-based security consultancy Seismic, plans to release a software tool at the conference later this month that he says could be used on about half the existing models of home routers, including most Linksys, Dell, and Verizon Fios or DSL versions. Users who connect to the Internet through those devices and are tricked into visiting a page that an attacker has set up with Heffner's exploit could have their router hijacked and used to steal information or redirect the user's browsing.

Heffner's attack is a variation on a technique known as "DNS rebinding," a trick that's been discussed for close to 15 years. "There have been plenty of patches over the years, but this still hasn't really been fixed," he says.

The hack exploits an element of the Domain Name System, or DNS, the Internet's method of converting Web page names into IP address numbers. (When you visit Google.com, for instance, a domain name server might convert that name into the IP address 72.14.204.147.) Modern browsers have safeguards that prevent sites from accessing any information that's not at their registered IP address.

But a site can have multiple IP addresses, a flexibility in the system designed to let sites balance traffic among multiple servers or provide backup options.

Heffner's trick is to create a site that lists a visitor's own IP address as one of those options. When a visitor comes to his booby-trapped site, a script runs that switches to its alternate IP address--in reality the user's own IP address--and accesses the visitor's home network, potentially hijacking their browser and gaining access to their router settings.

That DNS trick isn't new, and browsers have installed patches for earlier versions of the exploit. But Heffner says he's tweaked it to bypass those safeguards; He won't say exactly how until his Black Hat talk. "The way that [those patches] are circumvented is actually fairly well known," says Heffner. "It just hasn't been put together like this before."