If youre a Mac user and you downloaded this weeks Mac OS X update (Mavericks 10.9.3), you may have noticed that your computers Users/ and Users/Shared/ folders have disappeared. It turns out the disappearance is due to a security flaw in iTunes 11.2, which was part of the OS X Mavericks 10.9.3 update. The flaw is only really serious on iMacs and MacBooks with multiple user accounts, as it lets one account compromise the other accounts on the same computer.