Simone, users can block each other. Once blocked, a user will no longer be able to send IM/PM, become friends, follow and add comments to content of the block initiator. Blocking a user will immediately sever all Friendship and Follow links.
That is all we can suggest you now with the Block user functionality.
So, if you want to prevent the blocked user to view the profile of the other user this is considered as a custom code modification.
If you are not familiar with the plugin development or code modification, it would be better for you to find a developer who can help you. You can do it here:
http://www.oxwall.org/market/specialists .
And, you can make a suggestion on uservoice:
http://oxwall.uservoice.com/forums/13756-ideas-for-oxwall .