From what I've seen about these files they hold info about the challenges you've completed when logged in while playing the game to earn badges on the Sims 3 website.
Quick FYI: Came across this info while looking for something else in Sims Wiki:
dynamicchallenge "This file is downloaded to your computer when there's a new challenge/achievement available that you can do. It's unclear what happens if you delete the file. There might also be a new folder with a new very long number that only contains the ChallengeData.package".
grimsoul, I'm sure that the ChallengeData.package is referring to the explanation you offered. I never have played on line or even logged in until the other day when I was doing some testing. That must be when the files loaded advising there is a new challenge. Jeeze, I wish they'd stop loading stuff in my folders!