On Tuesday, Microsoft warned that it was issuing an emergency patch to fix a dangerous flaw in its software.
This is notable for a few reasons. Microsoft rarely releases these kinds of urgent patches, only nine of them so far in 2014. It normally saves all patches for one mega patch day once a month.
The software in question affects almost all of Microsoft's family of security software. That means that the software Microsoft designed to protect computers from hackers can be hacked. In this case, it can be turned off, and from there, the hacker could do more harm.