SAN FRANCISCO--A group of computer hackers on Sunday posted a document it claimed contains usernames and passwords for an Apple Inc. server, the latest in a string of brazen attacks that have compromised government and corporate websites around the world.

"AntiSec," a hacking campaign that includes hackers from both the online vigilante group Anonymous and hackers from the now-defunct Lulz Security, posted a document containing a link to a supposed Apple server along with a list of 26 administrative usernames and passwords....