LONDON: Malicious hackers brought down the Telegraph Newspapers website - one of Britain's largest online newspaper sites - on Monday and through most of Tuesday - using a 'denial-of-service attack' - a tactic that overwhelms a computer system and makes it unavailable to its intended users.

Warns Paul Vlissidis, technical director at security specialist NCC Group: "National newspapers are particularly high-profile targets, especially if they publish a story that someone doesn't like."

Most major websites can comfortably handle hundreds of thousands of requests daily, but DoS attacks are able to post as many as one million requests in five seconds. Such attacks are often powered by networks of computers or 'botnets', controlled by a single 'botmaster'.

It has been estimated that up to one in eight standalone PCs in the UK could unknowingly be part of a 'botnet' via malicious software covertly installed, for example, when visiting an infected website.

Although the Telegraph site was partially restored on Tuesday, it was still experiencing intermittent access problems at 18.00GMT.

Data sourced from; additional content by WARC staff