When you open your MySite for the first time, the following welcome dialog gets shown:
The by default checked “Let’s get social” option changes the privacy of all your social activities to “everyone”. It is easy that somebody clicks accidentally okay. In Germany most work committees don’t like the fact that this may could happen.
You can easily deactivate the such called first run experience through the following setting on the my site host’s web property bag:
Or via PowerShell:
$web = get-SPWeb http://mysitehost