To give you the exact "feature" or information you need, could you tell me:
You will need archive software like WinRAR or 7-Zip to look at the contents of a .rar file.
did you find "isus.rar" (e.g., inside a software folder, email attachment)?
"ISUS" sometimes refers to "InstallShield Update Service."
Here is what I can tell you about managing a .rar file like "isus.rar":