In some cases process may consume a lot of memory (over 100GB). Restarting service is a temporary solution.
Monitor Agent version 8.1 RU3
Corrupted file [C:\Program Files\Altiris\Altiris Agent\Agents\Monitor Agent\RuleState] is causing this problem.
Workaround:
1. Stop Altiris Monitor Agent service
2. Delete [C:\Program Files\Altiris\Altiris Agent\Agents\Monitor Agent\RuleState] file
3. Start Altiris Monitor Agent service