The bug, called WinShock, was first discovered by IBM in May, according to CNET, and has existed in every version of Windows since Windows 95.
Theoretically, WinShock could infect computers by tricking users into viewing a malicious website on Internet Explorer, which would then allow them access to your computer's code.
Luckily, IBM hasn't discovered any actual cases of attackers utilizing the security hole, and with the recent update to Windows, your computer should be safe once you update.
Microsoft's fix will already be applied if you have automatic updates turn on. If not, just make sure you install the most recent update to Windows on your PC and you'll be in the clear.