The attacker may have obtained partial, obfuscated copies of the MPEx databases. While I won’t go into details with regards to said obfuscation, it is a fact that breaching one proxy is not, as far as I can see, sufficient to obtain complete trade history. As directed in the FAQ, users are expected to take steps within their own control and at their own convenience to ensure their anonimity, and further,

    Internet-facing machines do hold copies of the database. They are reasonably secured, which probably means they are more secure than most any other bitcoin-based application at this time. However, their absolute security is not considered a strategic priority and no extraordinary measures are undertaken to ensure it.