"Comments were temporarily hidden by default within an hour [of discovering the problem], and we released a complete fix for the issue in about two hours. We're continuing to study the vulnerability to help prevent similar issues in the future," a Google spokesman said via e-mail.
The attack potentially put at risk YouTube cookies of users who visited a compromised page, but it couldn't be used to access their Google accounts, the spokesman said. As a precaution, YouTube users should log out of their account and log back in again.
The attackers apparently targeted singer Justin Bieber, incorporating code into YouTube pages devoted to him so that visitors saw tasteless messages pop up about the teen star, and were also redirected to external sites with adult content.
An industry source familiar with the situation said that while the attack itself didn't involve malware infections, such a risk is inherent whenever users visit any Web page, such as the ones attackers redirected users to. It's not clear if those landing pages contained malware, but most up-to-date anti-virus software is designed to protect against those threats, this person said.
YouTube is by far the most popular video uploading and sharing site. In May, U.S. residents watched 14.6 billion video clips at Google sites, mostly at YouTube. which is about 43 percent of all clips watched online that month, according to comScore.
On a day when the U.S. marks its independence with fireworks shows, social media sites like Twitter and Facebook lit up on Sunday morning with reports from thousands of individuals who noticed the YouTube hack.
A separate stream of postings on social media sites focuses on whether Apple's iTunes App Store may have been compromised by a rogue developer and whether purchases may have been made without victims' permission using their credit cards on file.
People posting about the Apple issue are suggesting that App Store customers check for any unusual activity on their accounts.
Apple didn't immediately respond to a request for comment from IDG News Service.
