DO sent me a CPU alert. I checked top and I see this for about 45 minutes now:

PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
18460 www-data  20   0  365576  81912  46836 S 21.2  8.0   2:35.30 php5-fpm
17378 www-data  20   0  347680  70084  52800 S 11.0  6.9  10:53.50 php5-fpm
18210 www-data  20   0  352256  72728  50884 S 10.0  7.1  10:14.65 php5-fpm

This is a web server running a few WordPress and Drupal sites.

I've checked Google Analytics and my visitors are not high for any site, there is never more than 1 or 2 online at a time according to Google Analytics Real Time reporting. Usually there are 0 users at any given time.

What should I do?

Is there any way I can see what is causing these specific PHP processes? Like which script or site somehow? I'm not sure how to diagnose this. My server has been running for 3 years, I always keep it updated, I've never had this happen and nothing out of the ordinary appears to be going on.

EDIT: I just updated a few plugins that had recent new versions on my 3 WordPress sites and the CPU usage immediately dropped to 0% or 0.3% as it is usually. Does it make sense that somehow a pending update would cause the CPU usage to spike for over an hour?