That seems to happen all the time, it's always false alarm. %wrd
Indeed, as
@Andreas mentions, Norton has a propensity for flagging any sort of executable created by a non-commercial author, often with generic "reputation-based threats", and occasionally, false flagging a file as a legitimate virus--Rontokbro is a particularly popular false positive.
We have been in the process of converting many of our installer-based downloads to plain .zip files, as part of the Project ZIP effort, not only because of the way the installers slow down the process of building a plugins folder, but because of the issues with anti-virus suites like Norton.
I've just given the Project ZIP treatment to the three files you linked, so Norton should no longer freak out with them, and you can just drop the contents directly into Plugins instead of running an installer.
-Alex