"ISUS" sometimes refers to "InstallShield Update Service."
You will need archive software like WinRAR or 7-Zip to look at the contents of a .rar file. isus.rar
are you trying to do with it? (e.g., scan it for safety, extract its contents, know what it belongs to)? "ISUS" sometimes refers to "InstallShield Update Service
did you find "isus.rar" (e.g., inside a software folder, email attachment)? scan it for safety
Here is what I can tell you about managing a .rar file like "isus.rar":
If this file was unexpected, downloaded from an untrusted source, or arrived via email, it is highly recommended to scan it with an antivirus program before opening it.