Hmm..in order for me to hack into someones messages i would have to delete my account now then log in with someone else's number right? I dont really wanna do that cuz i need quite a few messages. Work stuff. Anyway, i dont think its linked to the sim cuz my bf has 2 sim cards; one british and one german. So when hes in germany he puts the german sim in his phone but when hes on whatsapp its logged on with him brit number.. I only have his brit number saved on my phone so yea we're chatting as usual.. Another thing is that i lost my phone a while ago and got a new sim with the same number. I had gotten a second hand phone and logged into whatsapp.. Guess what nearly all my previous messages from my lost phone got uploaded back. I was glad about it cuz i have some of my friend's numbers back but then this led me to wonder how easy it is for someone to do the same using my number and retrieve my messages! What do u think?