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will this be rolled out to the older A6 or is this security hole only apply to A7?


As A6 is no longer supported and encryption may very well turn out to be a Lite C feature, I'm guessing you'll have to upgrade as encryption will not make it into A6 (since nothing new will make it into A6).

Which is not a bad thing considering that you get to make and send structs over the network with A7 and integration with other Net Libraries should you choose is more transparent in Lite C than C-Script.