The September Patch Tuesday update (released on second Tuesday of each month) makes a total of 105 Security Bulletins being released this year. The bulletins include five critical updates, out of which two address vulnerabilities in all versions of Windows. The reason for the increase in the total number of security bulletins within such less time might be because of Windows 10 release and its installation reaching to a score of 100 million. Microsoft rates the severity of the vulnerabilities and their impact on the affected software. Affected software includes Microsoft Office 2007, Microsoft Lync 2013 and Microsoft Live Meeting 2007.
Source: https://thehackernews.com/2015/09/windows-security-updates.html