Facebook, Twitter, Google, Dropbox, and other web services can be accessed by various applications and other services. Below are some links that can verify what external services have been configured to allow access.
Microsoft’s Live –> https://profile.live.com/Services/?view=manage
Dropbox –> https://www.dropbox.com/account#applications
Twitter –> http://twitter.com/settings/connections
The site MyPermissions.org http://mypermissions.org/ contains links for several different services not listed above.