Makers of the software used to connect computers on the Internet collectively released software updates Tuesday to patch a serious bug in one of the Internet's underlying protocols, the Domain Name System (DNS).

The bug was discovered "by complete accident," by Dan Kaminsky, a researcher with security vendor IOActive. Kaminsky, a former employee of Cisco Systems, is already well-known for his work in networking.

By sending certain types of queries to DNS servers, the attacker could then redirect victims away from a legitimate Web site -- say, Bofa.com -- to a malicious Web site without the victim realizing it. This type of attack, known as DNS cache poisoning, doesn't affect only the Web. It could be used to redirect all Internet traffic to the hacker's servers.

The bug could be exploited "like a phishing attack without sending you e-mail," said Wolfgang Kandek, chief technical officer with security company Qualys.

Although this flaw does affect some home routers and client DNS software, it is mostly an issue for corporate users and ISPs (Internet service providers) that run the DNS servers used by PCs to find their way around the Internet, Kaminsky said. "Home users should not panic," he said in a Tuesday conference call.

After discovering the bug several months ago, Kaminsky immediately rounded up a group of about 16 security experts responsible for DNS products, who met at Microsoft on March 31 to hammer out a way to fix the problem. "I contacted the other guys and said, 'We have a problem,'" Kaminsky said. "The only way we could do this is if we had a simultaneous release across all platforms."

That massive bug-fix occurred Tuesday when several of the most widely used providers of DNS software released patches. Microsoft, Cisco, Red Hat, Sun Microsystems and the Internet Software Consortium, makers of the most widely used DNS server software, have all updated their software to address the bug.

The Internet Software Consortium's open-source BIND (Berkeley Internet Name Domain) software runs on about 80 per cent of the Internet's DNS servers. For most BIND users, the fix will be a simple upgrade, but for the estimated 15 per cent of BIND users who have not yet moved to the latest version of the software, BIND 9, things might be a little more difficult.

That's because older versions of BIND have some popular features that were changed when BIND 9 was released, according to Joao Damas, senior program manager for the Internet Software Consortium.

Kaminsky's bug has to do with the way DNS clients and servers obtain information from other DNS servers on the Internet. When the DNS software does not know the numerical IP (Internet Protocol) address of a computer, it asks another DNS server for this information. With cache poisoning, the attacker tricks the DNS software into believing that legitimate domains, such as Bofa.com, map to malicious IP addresses.