In the most recent update of Jetpack, now at version 1.4.2, the Automattic team has worked on cleaning up some old code.
- Enhancement: Remove more PHP 4 backwards-compatible code (WordPress andJetpack only support PHP 5).
- Enhancement: Remove more WordPress 3.1 and under backwards-compatible code.
If you recall, PHP4 EOL was announced in 2010 with the what-was, upcoming release of WordPress 3.1. This was a huge win for the WordPress community as it provided a path to developing better and more cohesive code.
In the above changelog for Jetpack, the removal of backwards compatibility code to PHP4 and the removal of WordPress 3.1 code, is yet another win for efficiency in the plugin.
The Automattic team has done a great job of keeping Jetpack up to date and secure. There has only been one known exploit for Jetpack and it was patched quickly.