It appears that some Apple Mac Computers, ones bought over a year ago or earlier, may have a serious flaw that lets hackers sneak in undetected. The hack opens a backdoor that may enable the intruder to do something far more serious in the future. The hack was first discovered on 29 May 2015 and in the reports I have read linked below, Apple has not responded to queries.
The seriousness of this hack has been likened to the one at Sony Labs a few months ago when a large amount of corporate data was stolen. It is believed that the thread will only be for high level Mac users such as banks, company executives, the wealthy, politicians, journalists etc. In other words, most of us will be OK!