According to this new article
from Netcraft, PHP applications are becoming more and more at risk for hacking attempts.
Security holes in PHP-based content management and forum apps are an increasingly active front in Internet security, as hackers target unpatched weaknesses. The latest example is Monday's hack of chip maker AMD's customer support forums, in which an older version of Invision Power Board was compromised and used to distribute malware using the Windows Metafile (WMF) exploit.
While Windows flaws like the WMF vulnerability are useful to hackers assembling armies of compromised desktop computers, security holes in PHP applications provide access to more powerful servers hooked directly to high-speed network connections.
They go on to talk about the growth of CMSs that PHP has fueled - both the good and the bad - and how a less than religious application of patches to those CMSs can cause big headaches down the road.
It is good, though, that they make the distinction:
Most of the security issues with PHP-driven programs are found not in PHP itself, but rather in the libraries and applications built atop the server-side scripting language.