Jack Skinner has posted his latest "roundup" results of the most popularly installed versions of PHP across the web. In the post he looks through the percentage of installations for each version and how many are "secure" (currently supported and in a popular/stable linux distribution).
Last year, Anthony Ferrara posted an excellent round up of PHP versions in the wild, specifically focusing on the volume of un-patched versions running production websites. Even as an estimate it was an eyeopening moment for many people.
Using data from w3techs and, while the raw data isn't posted, what's there is good enough for an estimation. He talks some about the definition of "secure" in the context of the results and lists the current versions of several popular linux distributions and the versions they support. His results are then grouped by minor release and created some graphs for the results to help with visualization. The remainder of the post shares these results for PHP versions 5.6, 5.5, 5.4, 5.3 and yes even 5.2/5.1. The results end with overall numbers/graphs of the most widely installed versions and what percentage of those are considered "secure". With PHP 7 just released the results are a little discouraging but it is good to see things trending the right way since last year's results.