Comment 5 for bug 302314

To correct my previous comment (https://bugs.launchpad.net/ubuntu/+source/pidgin/+bug/302314/comments/3), the path to place the login.live.com certificate (or any other certificate you want Pidgin to accept per-user) is
~/.purple/certificates/x509/tls_peers/

Sorry for the confusion. I was thinking of /etc/ssl/certs instead. You probably don't want to just dump certificates in there.

To emphasize, making symlinks in your home directory or dumping trusted certificates in ~/.purple are just crude short-term workarounds to avoid accepting untrusted certificates because of a bug. They aren't long-term solutions.

komputes: I haven't had any issues with rsi.hotmail.com, though according to http://developer.pidgin.im/ticket/6680 you might have offline messages that aren't getting through. Apparently MSN uses a different host and a different certificate for offline messages. Until an official fix for Ubuntu is released you could perform the Firefox workaround I suggested above for login.live.com with rsi.hotmail.com, or you could find another way to verify the certificate (there are some instructions on using openssl and a certificate in the Pidgin ticket; it appears to be out of date though), or you could just accept the certificate if you're feeling lucky (though I wouldn't recommend it).