Sharepoint 2010: search results display files where users have not access

On our SP2010 system, the users are able to find files where they have not the rights to access.

Here is an example. In a document library we created a TEST folder where we put the "link.txt" file. Only "User 1" has "full control" on it.

https://dl.dropboxusercontent.com/u/13948046/stack/permessi%20cartella.jpg

If we check "User 2" rights on the file, we can see "User 2" has no rights on it. But "User 2" is able to display it in the search results:

https://dl.dropboxusercontent.com/u/13948046/stack/2%20check%20permission.jpg

Then if "User 2" clicks on the file link, he receives an "access denied" message. Thank you for your help.