A group of 7 researchers have been able to successfully hack an MD5 encrypted security certificate. While this is a critical security risk, most security certificates do not use MD5 encryption in their generating processes. The more common security certificate and digital signature encryption type is SHA-1. One thing you’ll note is that the attack is on PKI as MD5 is a crypto hashing algorithm and not an encryption type.
The full explanation of their findings can be read at http://www.win.tue.nl/hashclash/rogue-ca/.