Microsoft releases Security Patches the 2nd Tuesday of each month. This is known as "Patch Tuesday.' Microsoft will release new versions of older patches. Below are links to information regarding the Microsoft Security Bulletins
Microsoft Security Bulletins
Latest Microsoft Security Bulletin Data (updated every month)
There are 2 files that download in the above data.
1. Excel file that contains affected software, bulletin replacement, reboot requirements, and CVE information from the Microsoft security bulletins (since June 1998)
2. Zip file that contains security bulletins in the Common Vulnerability Reporting Framework (CVRF) format (since June 2012)