The Italian branch of the hacking collective claims that the cyber attack was a stand against the "corruption" of the Roman Catholic Church.
"Anonymous decided today to besiege your site in response to the doctrine, to the liturgies, to the absurd and anachronistic concepts that your for-profit organisation spreads around the world," read a statement on the group's Italian website.
"This attack is not against the Christian religion or the faithful around the world but against the corrupt Roman Apostolic Church."
The incident follows reports that the FBI has brought charges against an alleged member of Anonymous, and members of its sister group LulzSec.
A spokesperson for the Vatican revealed that its official website was inoperable yesterday evening, but said that it could not be confirmed whether this was a result of hacker activity.
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