How to get information about Magento security patches?

Unfortunately there was no public blog post or news (at least that I know about).

So the best ressource is definitely getting on the Magento Partner mailing list, where this was first announced. I don't know if you can subscribe to it without being a partner.

But besides that it was also tweeted on the official Magento Twitter account: https://twitter.com/magento

In my opinion that's not the best way to communicate things like these, but at least another ressource to get relevant updates.

Magento has very recently launched the Security Alert Registry—a mailing list that receives updates every time there's a potential security vulnerability or Magento patch.

Sign up here: http://magento.com/security

the official twitter account doesn't always alert about patches, take SUPEE-5944 for example. their is also no options on the magento site to subscribe for this kind of notifications. I've set up an alert on google.com/alerts ("magento patch supee-"), it eliminates a lot of background noise