Updated, 9:40 p.m. to add YouTube's explanation of what caused outage.
YouTube suffered a two-hour long, system-wide outage on Sunday that the company said was triggered by a network based in Pakistan.
"For about two hours, traffic to YouTube was routed according to erroneous Internet Protocols," said YouTube spokesperson Ricardo Reyes in a statement "Many users around the world could not access our site. We have determined that the source of these events was a network in Pakistan. We are investigating and working with others in the Internet community to prevent this from happening again."
The BBC reported that Pakistan's attempts to block access to YouTube may have inadvertently caused the outage. Earlier in the day, Pakistan's shutoff access to YouTube inside the country in response to the posting of cartoons of the Prophet Mohammad, which have outraged many Muslims.
The BBC Web site's technology editor, Darren Waters, says that it's likely that--to prevent Pakistan's residents from accessing the site--Pakistan Telecom hijacked YouTube's IP and passed that information on to the country's Internet service providers so that queries to YouTube would be redirected. However, the details were apparently leaked by Asian ISP PCCW, leading Internet service providers around the world to mistakenly block YouTube, the BCC reported.
Engineers at YouTube were able to lift the blockade after contacting PCCW, according to the report.
"This was probably a simple mistake by an engineer at Pakistan Telecom," an unidentified "leading net professional" told the BCC. "There's nothing to suggest this was malicious."
Keynote Systems, a company that measures Web site performance, first logged YouTube's outage at 10:48 a.m. PT, and the site did not come back online until about 12:51 p.m.
Attempts to log on to the Google-owned site typically timed out. Keynote is unable to uncover the causes of an outage, said Shawn White, Keynote's director of operations, but he added that he would be shocked if one country had the ability to bring down YouTube globally.