San Francisco - Cyber attacks hammered Twitter, Facebook, and Google on Thursday, disrupting the hip micro-blogging service and causing stumbles at the hot social-networking site while Google fended off assaults.
Twitter was down for more than an hour early in the morning, before the eponymous California firm got it back online.
"The continuing denial of service attack is being mitigated, although there is still degraded service for some folks while we recover completely," Twitter co-founder Biz Stone said in an official company blog.
"Twitter has been working closely with other companies and services affected by what appears to be a single, massively coordinated attack. As to the motivation behind this event, we prefer not to speculate."
By late afternoon, Twitter said that service was improving but was still sporadic, with some people "unable to post or follow from the website."
Facebook was "degraded" by an early-morning distributed-denial-of-service (DDoS) attack on the Palo Alto, California-based Internet star's website, said spokeswoman Brandee Barker.
"No user data was at risk and we have restored full access to the site for most users," Barker said. "We're continuing to monitor the situation."
Twitter and Facebook have teamed with US Internet powerhouse Google to investigate the attacks.
Cyber attacks were launched on Google websites, but the firm deflected the assaults.
"Google systems prevented substantive impact to our services," said company spokesman Nate Tyler.
"We are aware that a handful of non-Google sites were impacted by a DOS attack this morning, and are in contact with some affected companies to help investigate this attack."
Hackers evidently employed classic DDoS attacks in which legions of zombie computers, machines infected with viruses, are commanded to simultaneously visit a website.
Such a massive onslaught of demand can overwhelm website computer servers, slowing service or knocking it offline.
"Ten years ago, we saw the first DDoS attacks take down some of the world's largest websites," said Cisco chief security researcher Patrick Peterson.
"The irony here is that botnets, infected criminally-controlled consumer PCs, are the problem. Many of today's tweetless are part of the attack if their PC has been infected due to poor security."
A DDoS attack hit Twitter about 14:00 and caused the service to go offline temporarily.
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.
The attack was the lead topic of conversation at Twitter, once users were able to reconnect.
Twitter user Benjamin Hobbs fired off a message saying he "wishes the denial-of-service idiots would get a life and leave Twitter alone."
Late in the evening, users were still posting comments in droves about the attack, using the tag #whentwitterwasdown, although many said they simply did not notice.
Freedom of speech, expression
An everyday chatting tool for many, Twitter has also become a weapon for dissidents to circumvent censorship in places where freedom of speech is suppressed.
Independent information about deadly riots in China's remote northwest filtered out on Twitter, YouTube and other Internet forums in July, frustrating government efforts to control the news.
Similar to the phenomenon seen a month earlier during Iran's political turmoil, pictures, videos and updates from Urumqi poured onto social networking and image sharing websites like Twitter, YouTube and Flickr.
In many cases, items were reposted by other Internet users on sites outside China to preserve the content, while Twitter helped link people around the globe to images Chinese authorities did not want seen.
Cyber-sympathisers from around the world joined forces through Twitter in June to help Iranian protesters dodge censorship, get out news of violent clashes and avoid real-world capture following Iran's disputed election that returned hardline President Mahmoud Ahmadinejad to power.
Cyber attacks on Web pages of Iranian opposition figures have continued in the aftermath of the controversial presidential election.
-AFP