The phrase, "are believed to be", should never ever be in allowed in a news article unless your source would be in some sort of danger. Even then, you should give some reference to the validity of the source. They might as well be reporting what a magical 8 ball told them when they asked it about the hack. This is especially so if it's the lynchpin of your headline.
The passive voice tends to annoy me, especially when writers employ it without an agent. I make an exception for scientific texts, but only begrudgingly.