Restricting User Access to Group Information

[Jack Hollingsworth]

We have formed a number of groups with individuals, and don't want individuals to be able to access information (files, blog info, etc.) from any group the individual is not a member of.  

When I log in as an administrator, and then log in as a user, I can search from the left hand drop down, files that belong to another group that the user is not a member of and access the detail of those files. 

I want this stopped.  How can it be done? 

Jack