Microsoft doesn't exactly have a good reputation to begin with in this field.
Some years ago it was common that your messages through Live Messenger (and Windows Messenger when it was still called so) got censored in real time. In one case any message containing the string "download.php" never reached the receiver and another time the same was true if your message contained a link to the piratebay or simply the phrase "live messenger". I can't remember any more concrete examples but there were many times you could easily figure out the pattern.
Some years ago it was common that your messages through Live Messenger (and Windows Messenger when it was still called so) got censored in real time. In one case any message containing the string "download.php" never reached the receiver and another time the same was true if your message contained a link to the piratebay or simply the phrase "live messenger". I can't remember any more concrete examples but there were many times you could easily figure out the pattern.