Yes - I have always used "Share with account" but I have also tested without. But thanks alot for the info - I have disabled Samba sharing for the moment. It was indeed accessible from WAN. Eventhough the shares were password protected I didn't trust the security completely - better safe than sorry. I will await an updated version of the firmware and see if that solves my issue.
Although it's probably unrelated to your problem, I'm glad I could make you aware of the potential security issue. The security issue is not only dumbfounding, but also troubling.