You can view the contents of PMs by simply looking in the database. All this MOD does is simplify the process.
No words are more true if you are sincere about privacy.
Off the top of my head (mine is worded a bit more strong than a general notice)...
This site has enhanced capabilities to investigate claims of abuse in other-than-public areas. These features are utilized only in the event of a claim made to the moderators or administrators of the site. If harassment is found in these areas your account may be suspended/banned.