Apple sends out virtual "blacklists" to Internet-connected Macs, instructing them not to run certain programs. Apple is blocking the latest version of Java from running on the most recent versions of its Mac operating system, and blocking an older version, Java 6, from running on the older version of its Mac system, called Snow Leopard. The blocks affect programs and online games that use Java in Web browsers.
Oracle had no immediate comment on Apple's action.
Among those Java users inconvenienced by the unannounced block was the photo department of The Associated Press, which relies on a Java application to manage and distribute photos.
"The situation caught us by surprise and a number of our machines could not operate for a time, but we had enough capability to work around the problem in the meantime," said AP spokesman Paul Colford. "We expect the affected machines to be operating by day's end."