In rare instances there has been an issue on 9.0 - 9.1 sites with device detection set to true where CPU usage quickly escalates to near 100%. Due to the high consumption of resources a thread abort error is given and the application pool may crash.
To identify if this is your issue, please check the following:
1. Check your device detection value. Identify if it is set to true.
2. Check your event viewer logs. Check under "Windows Logs" > "Application" for thread abort errors. If you see these errors, look for references to 'wurfl.manager' in the stack trace.
If you are seeing both these values, the below resolution should apply. If you are not, please check out the performance KB .
This is a documented issue in our 9.1SP1 site cumulative update release notes.
If you are not using mobile device detection, Ektron's adaptive imaging or you do not have a license with Scientiamobile, Inc. in order to use WURFL, please see the following KB for more on WURFL licensing, how to remove WURFL, and to see the alternative.
If you are using device detection and you notice this issue, apply cumulative site update 7 or later for 9.1SP1. If you are still seeing issues, please contact support.