IDK why they would be scanning ports, I keep all unused ports closed on my systems.
The scan is probably benign. I mean, everyone is trusting them with their credit card info, or trusting that their paypal link isn't harvesting their password, so I wouldn't worry about it.
Every deal I've done with Rendo has ended well, and I've found them more than helpful with any problem, so I pretty much trust them.

You can worry about it, I guess, but I'm not. Anyway, it's been my experience that Norton usually causes more problems and confusion than it ever cures.

FWIW