Restricting the usage of Extensions
We have been talking about this for a while, but it is important to repeat. Limit your usage of extensions (or plugins), along with all other third party components, and only use from trusted sources. More importantly, only if you need the said functionality. The less plugins you have configured in your environment, the less chances you have to be caught in a similar situation. The last thing you want is to become part of a SPAM botnet.