There are some threats that impersonate legitimate programs, modify browsers or the boot screen graphics, and even redirect traffic. Our standard scanners necessarily have a delicate balance between effective malware detection and removal and erroneously removing legitimate files. Sometimes, these "scareware" programs can require special tactics to remove them. With the Norton Power Eraser tool, these threats (and others) are specifically targeted, and thus are effectively detected and removed.
You should use the Norton Power Eraser tool when nothing else will remove an annoying program and you are willing to accept a higher risk that the scanner may quarantine a legitimate program.
Because the Norton Power Eraser uses aggressive methods to detect these threats, there is a risk that it can select some legitimate programs for removal. You should use this tool very carefully, and only after you have exhausted other options.