Both Twitter and Facebook have been subject to some extreme attacks in the past few days from online hackers who are targeting these high profile social networking sites with the aim of causing disruption to their service. As reported by the BBC, Twitter was taken offline for more than two hours whilst Facebook's service was "degraded" as both sites were subject to so-called denial-of-service attacks.

These attacks can take various forms but often involve a company's servers being flooded with data in an effort to disable them. Such attacks often use networks of computers - known as botnets - which are under the control of hackers, often as the result of previous viral attacks or 'Trojan horses' that have infected computers around the world. The strategy is often employed by protestors against, for example, government websites or to disrupt high profile sites for publicity.