Hi there, This is a false positive. I run the installer through 43 different virus scanners. Here are the results: https://www.virustotal.com/en/file/...41142066df823beaa04a36f5daeffe090ad/analysis/ As you can see, even Symantec (the company that created Norton) doesn't pick it up. There is no need for concern.
I haven't used Norton since 2005, so I can't really help with that. There should be an option to disable the anti-virus or exit the program by right-clicking on the Norton icon in the system tray. Try that, install Pokemon Online, delete the installer, then reopen Norton. If that fails, Google is your friend. :)