On the Paragon Initiative blog they've posted a guide to handling automatic security updates for PHP developers, helping to prevent security-related issues by keeping your libraries up to date.
Most of the software security vulnerabilities known to man are preventable by careful development practices. [...] However, even if you're trying to do everything right, eventually we all make mistakes and ship exploitable software.
[...] By making updates manual rather than automatic, you're forcing your customers to take all the responsibility for making sure that your mistakes don't hurt their business. Only a very small minority of your customers might prefer the responsibility of verifying and applying each update themselves. [...] Automatic security updates reduce the interval between points 2 and 3 from possibly infinite to nearly zero. That's clearly a meaningful improvement over manual patch management.
The post then walks through the aspects of a secure automatic update system that includes offline cryptographic signatures, transport layer security and separation of privileges (who will perform the actual update). The author gets into a bit of detail for each item on the list, explaining how the system should be set up and some tools you can use to start working up the process in your own applications.