I read this on a blog:

"The answer is that segwit uses what is, in my professional opinion, an unthinkably nasty hack: according to the Bitcoin protocol, all segwit transactions can be spent by anybody with no proof of authorization. That means that literally anyone can make a transaction that spends the bitcoins in a segwit address. The "witness data" (which is the rules for who's allowed to claim the outputs, and the proof that the rules were followed on the inputs that claim the outputs) is moved out of the main block and replaced with a simple "anyone can spend me, there are no rules and no proofs," and it's up to miners to know what the rules really are, ignore the "anyone can spend me" instruction, and instead apply the rules from the witness data."

can someone explain further?
do i need to change my wallet in my ledger nano S from Segwit to Legacy?