Troj/Istsvc-A is a Trojan downloader for the Windows platform.
When installed Troj/Istsvc-A periodically attempts to download and run files from the Internet while running in the background as a service process.
Troj/Istsvc-A then creates the following registry entry so as to run itself on computer logon:
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
<random name>
<path to Trojan>
Troj/Istsvc-A also creates the following registry entry:
HKCU\Software\IST\