YNOT – YouTube giveth, and YouTube taketh away — sometimes with help from hackers.On Sunday morning, a group of unknown hackers attacked Google’s tube site, inserting code that variously redirected users to porn sites or spread rumors that Canadian 16-year-old pop singing sensation Justin Bieber had died in a car accident. The irony? Bieber’s career took off after a series of his YouTube videos came to the attention of R&B superstar Usher, who helped Bieber land an agent and then a lucrative recording contract.

According to published reports, hackers took control of the viewer-comments component of Bieber’s YouTube pages through a cross-site scripting vulnerability. Inordinately popular with teenage girls, Bieber’s videos reportedly receive millions of hits monthly.

Internet forum 4Chan is believed to have launched the attack, but other hacker groups may have joined the assault once it was underway. A Google spokesman said the breach was repulsed within hours, no user accounts were compromised and no malware was distributed. However, viewers who were redirected to porn sites may have encountered drive-by malware or phishing schemes when they landed, a source told news service IDG.

“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,” Google said in a prepared statement. “We’re continuing to study the vulnerability to help prevent similar issues in the future.”

As for Bieber, he assured fans he’s still alive and kicking butt in the music industry.