AMR- Yes, if you use the product you should turn the Immunization function on. The important thing that it will block will be malware that puts itself in AppData and tries to run from there.
As to the %Startup% reference- this really means stuff in the Users\your name\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup directory. Actually not much ever gets places in there; you can check what is included on your computer by just going to Start-All Programs-Startup. This will show you what is on your system that will be blocked if you immunize.
Remember well that quite a few Encryptors will just start from other areas and will sidestep this protection (like CryptoFortress). One other REALLY important thing is that if you are storing documents anywhere else other than C:\Users\your name\Documents they WILL NOT be protected. many people with SSD drives will move things like mp3, photos, etc to another drive and are surprised when they get zapped.
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