Why computers in the new discovered subnet are under "Installed Agent" catagory (No scheduled Agent installation task)? (Screen attached)

Hi,

I have a All-in-One Altiris Notification Server 7.5 (Virtual Machine) for PC inventory & software deployment with MSSQL database 2008 R2.

I run a IP subnet discovery and some new computers are found. However, I found those computers in the new discovered subnet are under "Installed Agent" catagory  (No scheduled Agent installation task).

I would like to know:

1) Why those computers would be undered "Installed Agent" catagory without agent installed task is run?

2) I found those computers icon are different from the others, what does it mean?

Thanks.