Facebook users were surprised yesterday to find the site suffering from some rare downtime.

Service failures on Facebook began early Thursday morning and continued throughout the day. Outages for the site were seen as late as 6am PST the following morning.

"Some users briefly experienced issues loading the site," Facebook said in a statement regarding the outage.

"The issues have since been resolved and everyone should now have access to Facebook. We apologize for any inconvenience."

Facebook has not offered an explanation for what caused the typically smooth operating site to lose service.

An attack or internal?

On the other hand, notorious hacker collective, Anonymous, appears to offer an explanation by taking credit for Facebook's downtime.

During the outage the YourAnonNews Twitter account yesterday posted the message, "Looks like good old FaceBook is having packet problems… #F***FaceBook | #OpFaceBook | #F***YourIPO."

It was followed an hour later by a second tweet, "Oh yeah… RIP Facebook a new sound of tango down ..."

If the purpose of the attack was to damage Facebook's newly launched IPO, then it worked.

The Facebook IPO is currently $1.85 down, or 6.25 percent, from its closing price yesterday.

However, despite the claims from Anonymous, there is still some doubt.

A Facebook spokesperson said, "I can confirm that yesterday's issues were not the result of a denial-of-service attack."

Direct denial of service (DDoS) attacks have historically been the Anonymous group's primary tool against its targets. If the cause wasn't from a DDoS attack then an internal issue may be to blame.

Facebook still hasn't issued a statement on what caused service outages yesterday.