Officials fear social networking sites allow inmates to keep offending while behind bars.
Matthew Cate, secretary of the California Department of Corrections and Rehabiliation, said in a statement on the CDCR website that "access to social media allows inmates to circumvent our monitoring process and continue to engage in criminal activity."
Though holding a Facebook account isn't a violation, neither inmates nor a third party are allowed to update their account until finishing their prison sentence.
Facebook spokesman Andrew Noyes told ABC News "If a state has decided that prisoners have forfeited their right to use the Internet, the most effective way to prevent access is to ensure prisons have the resources to keep smartphones and other devices out."
Officials point to one California incident where access to social media allowed an inmate to harass a former victim. After his conviction for child molestation, he found the 17-year-old girl's photos on Facebook and MySpace. This information allowed him to draw pictures of her and mail them to her home address.