(There's no video for Vaccine yet. Please contribute to MR and add a video now!)
Vaccine warns you whenever certain significant resources are being modified. You can grant permission for the change to take place (if you're running an installer program for example), but you're in control
When a vulnerable resource is m=being modified, the menu bar blanks and a small icon appears on the far right. Either click the tiny yes/no to proceed, or click the icon to get a larger dialog with details of the modification.
Vaccine1.0.1.sit (6.07 KiB / 6.22 KB)
System 1 - 7 / compressed w/ Stuffit
Emulating this? It should run fine under: Mini vMac