April’s Microsoft Windows update has apparently been causing headaches for users who had previously installed anti-virus software from vendors such as Avast, Avira, ArcaBit, McAfee and Sophos. Users with these AV products who installed the 9 April Windows update may find that their machines become slow or unresponsive following restart, according to the “Known Issues” section of Microsoft’s Monthly Rollup update web page.
Source: SC Magazine UK