(CNN) -- Change.org was hacked late Friday by someone who made "cosmetic" changes on the popular petition website, officials said.
No personal information was stolen, spokesman Benjamin Joffe-Walt said in a written statement. He added that none of the 12 petitions targeted had its number of signatures affected.
The modified petitions included one calling for officials to end the prosecution of a Florida teen charged in connection with a same-sex relationship with a 14-year-old; a petition to close the detention center at Guantanamo Bay; and a petition to allow gay Boy Scouts leaders, said Brianna Cayo-Cotter, a spokeswoman for Change.org.
Change.org officials believe the petitions were selected because they were all in a featured section of the website and weren't picked because of the causes they represent, she said.
Joffe-Walt said the hacker exploited a "minor vulnerability" and made changes to text and photos on the petitions. The flaw was fixed while the website was offline, he said.
Change.org, based in San Francisco, California, says it has 35 million users in 196 countries.
Successful Change.org campaigns have included one in which a petitioner asked Bank of America to rescind a $5-per-month fee on bank cards. The petition received more than 300,000 signatures and helped to spark wide media coverage.
CNN's AnneClaire Stapleton and Devon Sayers contributed to this report.