system
8
http://news.softpedia.com/news/Microsoft-KB2859537-Update-Causes-BSODs-Due-to-Avast-Incompatibility-377488.shtml
Microsoft’s KB2859537 update released on Patch Tuesday is causing lots of problems on Windows 7 computers, with some users now reporting issues due to incompatibility with Avast anti-virus software.
http://news.softpedia.com/news/Microsoft-Pulls-Botched-KB2859537-Windows-7-Update-377356.shtml
If you have this installed-remove it if you want a better computing experience. MS has pulled it along with 4 other ones.