Early this morning, the Twitterverse was silenced by a major denial-of-service attack. Although the service is functioning normally again, its admins are apparently still fending off the attack.

At about 10 AM EDT, Twitter posted the following update to its status page:

Site is down

We are defending against a denial-of-service attack, and will update status again shortly.

Update: the site is back up, but we are continuing to defend against and recover from this attack.

Co-founder Biz Stone said in a blog post:

“On this otherwise happy Thursday morning, Twitter is the target of a denial of service attack. Attacks such as this are malicious efforts orchestrated to disrupt and make unavailable services such as online banks, credit card payment gateways, and in this case, Twitter for intended customers or users.”

Twitter has, of course, gone down plenty of times before, but it has become way more reliable in recent months, partly because it switched its code to a programming language called Scala. Yet, this is the first time that such a major outage has been caused by a deliberate attack.

While it’s hard for even the biggest sites to defend against a distributed denial-of-service attack launched by a major botnet, this certainly won’t help Twitter’s efforts to position itself as a critical communications platform.