Microsoft is pushing yet another security update to members of the Windows Insider programs on Windows 10 build 10240. The update's support number clocks in at KB3074683, but we don't have anything in the way of details concerning what the security update addresses.
We've seen a number of these updates over the last week, with the last coming in just yesterday. These are likely meant to address some issues just ahead of Windows 10's launch, which is due in just a couple of days on July 29.
Thanks to Gareth for the tip!