Troj/Agent-DS is a proxy Trojan with backdoor functionality for the Windows platform.
Once executed Troj/Agent-DS copies itself to the Windows system folder with the filename scrsvc.exe, and in order to be able to run automatically when Windows starts up sets the registry entry:
HKLM\Software\Microsoft\Windows\CurrentVersion\Run\
scrsvc
scrsvc.exe
Troj/Agent-DS modifies a Windows HOSTS file prepending it with the list of the popular search engine sites looped to the specific IP address.