https://np.reddit.com/r/Buttcoin/comments/6ndfut/buttcoin_is_decentralized_in_5_nodes/dk9c27f/
Core/Blockstream/Greg Maxwell explained. Great post by JStfolfi (np.reddit.com)
submitted 6 days ago by jonald_fyookball

jstolfi 160 points 6 days ago*

SegWit is another messy imbroglio that resulted from that pile of lies. The "malleability bug" is a flaw of the protocol that lets a third party make cosmetic changes to a transaction ("malleate" it), as it is on its way to the miners, without changing its actual effect.

The malleability bug (MLB) does not bother anyone at present, actually. Its only serious consequence is that it may break chains of unconfirmed transactions, Say, Alice issues T1 to pay Bob and then immediately issues T2 that spends the return change of T1 to pay Carol. If a hacker (or Bob, or Alice) then malleates T1 to T1m, and gets T1m confirmed instead of T1, then T2 will fail.

However, Alice should not be doing those chained unconfirmed transactions anyway, because T1 could fail to be confirmed for several other reasons -- especially if there is a backlog.[//b]

On the other hand, the LN depends on chains of the so-called bidirectional payment channels, and these essentially depend on chained unconfirmed transactions. Thus, given the (false but politically necessary) claim that the LN is ready to be deployed, fixing the MB became a urgent goal for Blockstream.