PC users are being warned that they may unknowingly have contributed to a massive attack by hackers on the root servers of the Internet yesterday.

On Tuesday morning three major servers that help send internet traffic around the globe came under attack from hackers.

The malicious coders sent a flood of data to the servers in an attempt to overload them. Had they succeeded, it would have meant web sites would be unreachable and delivery of e-mail messages would be suspended.

However, experts believe the attack was unsuccessful due to the robustness of the server machines, and the work done by server operators to prevent any disruption to Internet users.

Some security experts believe hackers may have used a network of 'zombie' computers in the attack - PCs owned by individual users that have been infected with malicious code, allowing intruders to take them over and use them to send junk data to the servers.

PC users are being urged to keep their computers protected with security software including anti-virus and firewalls.

Related Tip: 5 Steps To Keep Your PC Safe Online