A Palestinian hacker posted a message on Facebook founder Marc Zuckerberg’s wall to show there is a bug in the social network’s security settings.

Khalil Shreateh of Hebron posted information about the bug on Zuckerberg’s wall late last week, following unsuccessful attempts to report the bug to Facebook security. The bug allowed Shreateh to post on the walls of other members despite security settings.

“Sorry for breaking your privacy … I had no other choice … after all the reports I sent to Facebook team,” Shreateh wrote on Zuckerberg’s wall.

Facebook security had denied that the flaw was a bug.

Shreateh, who is unemployed, had hoped to win a $500 reward paid out to hackers who discover bugs on Facebook. Instead, his Facebook account was frozen, since he violated Facebook’s terms of service by posting illegally on Zuckerberg’s page. His account has since been reinstated.

Zuckerberg has 18 million friends on his Facebook page.