php5-cgi huge memory usage

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I have the same problem for two days now.

Code:

vu2012    4374 77.8  0.1  81060  7940 ?        R    Oct26 626:20 /usr/bin/php5-cgi
vu2012   27454 52.2  0.1  81124  7992 ?        R    03:13 176:46 /usr/bin/php5-cgi
vu2012   27792 44.0  0.1  81088  7956 ?        R    03:53 131:19 /usr/bin/php5-cgi
vu2012   28747 33.5  0.1  81100  7992 ?        R    05:26  68:47 /usr/bin/php5-cgi
vu2012   29436 31.6  0.2  82100  9000 ?        R    06:23  47:01 /usr/bin/php5-cgi

The problem is that it uses a lot of cpu. I could kill them manually, but this wont stop it from happening again. Server has an uptime for 59 days and I didnt change anything but it started yesterday. I rebootet the server and I have the same problem today (yesterday there where a lot more processes, the server had a load average of 22 - 4gb ram amd 2 cpus debian etch, ispcp 1.0.6).

All the processes belong to the same virtual host.

Any ideas how to prevend this from happening?