Back around 2005-2006, I discovered this blocking thing that Microsoft does when I tried to send a friend a link to a page on my website. It was blocked with that same “The link you tried to send was blocked because it was reported as unsafe.” message.
It wasn't targeted at my website specifically, it was targeted at ALL .info domain names, regardless of the content of the website.
I don't know if they still do that. I haven't used MSN in quite awhile.
I also recall there being a default setting in the options that a user could change to remove the block. I do remember having to do something in the options to allow me to send links to my site to people and they had to do the same to be able to receive them. Again, I don't know if that is still the case and if it is still user configurable.
It was supposed to prevent malware from spamming everyone in your contact list with malware URLs, in case you became infected.
It is possible that it's not a piracy related censorship issue and that a lot of people have been uploading malware torrents to TPB, that once installed on a user's system will spam everyone in their contact list with the URL to get the torrent (among other things)...lather, rinse, repeat, and all your friends that trust you are infected, and their friends, and their friends, and so on....without the malware writer having to spend a dime to buy a domain name or for hosting, and no worries about his site getting shut down. Once he uploads his torrent and seeds it, it's self perpetuating....unless someone like Microsoft does something to block it.
If this is the case, then Microsoft may well be justified in adding TPB to their block list.