securityd goes nuts every 4 minutes & 30 seconds
You are facing a continuous flow of information messages.
This flow is truncated by chunck of 500, which is the default value of
mps_limit in /etc/asl.conf. This means that your flow of security related messages is at a rate > 500 / s. This is huge.

Could you open:

/var/log/secure.log
/var/log/kernel.log


and check which message could be related with this continuous
flow of information messages?

Could you type the following command (in an xterm or Terminal window):

top -o msgsent


to check if the culprit could be a local process and tracked down through its huge level of messages sent? You will have to enlarge
your window to more than 152 characters large to see the film.