Question
What is the AexAgentUIHost.exe process?

Answer
This process hosts the system tray icon for those computers logged onto the NS via terminal services. In addition, you will see one instance of this process for each user logged on to the system.

There is a registry key setting that can keep AexAgentUIHost.exe from loading for each user:

HKLM\Software\Altiris\Altiris Agent\Run UI in main Session only

Changing the value to 1 will keep the process from loading for every user.

Restart the Altiris Agent (NS 6) or Symantec Management Agent (NS 7) Service on the server

153093 "User session gets hang when login off from Citrix server"