Twitter down after 'malicious' cyber-attack

Hackers knocked wildly popular micro-blogging site Twitter offline for several hours Thursday with a malicious cyber-attack on its systems, according to the company's founder. Hot online social networking service Facebook was also reportedly experiencing woes and trying to root out the cause. Twitter was down for more than two hours before engineers at the California firm were able to get it back online with a warning at the website that "we are continuing to defend against and recover from this attack." Hackers evidently employed a classic denial-of-service (DoS) attack in which legions of zombie computers, machines infected with viruses, are commanded to simultaneously visit a website. Such massive onslaught of demand can overwhelm website servers, slowing service or knocking it offline. Access to the website continued to be slow, with some aspiring users getting messages telling them that connections had "timed out" because Twitter computers were taking too long to respond.