aMSN (aka Alvaro's Messenger) 0.96 and earlier allows remote attackers to cause a denial of service (application crash) by sending invalid data to TCP port 31337.

aMSN: Improper SSL certificate validation (MITM) when connecting to the MSN server

aMSN (aka Alvaro's Messenger) 0.98.3 and earlier, when SSL is used, does not verify that the server hostname matches a domain name in the subject's Common Name (CN) field or a Subject Alternative Name field of the X.509 certificate, which allows man-in-the-middle attackers to spoof an MSN server via an arbitrary certificate.