Parity Technologies’ Parity multi-sig wallets that were deployed after July 20 contains a severe vulnerability that makes it impossible for users to move their funds out of those wallets. The vulnerability was triggered by a regular GitHub user, “devops199,” who accidentally removed a critical library code from the source code that turned all Parity contracts into a regular wallet address and made the user its owner. Devops199 then killed this wallet contract, making Parity multisignature wallets tied to that contract instantly useless.
Source: https://thehackernews.com/2017/11/parity-ethereum-wallet.html