Applies to Windows Vista and Windows 7

Error Message: The installation of Sophos Anti-Virus has failed (error 0x80041f09)

The first thing to check is whether the User Access Control is enabled; kindly disable and try re-installing Sophos

Control Panel - Users Accounts - Change User Account Control Settings

In most cases; the above step should get you through; if not look no further beyond the below link

http://www.sophos.com/en-us/support/knowledgebase/1462/8450/8550/13418.aspx