Virtual currency wallet company Parity Technologies froze 600,000 ETH or approximately $150M upon disclosing multi-signature ETH wallets on November 8. Parity discovered the feasibility of turning the Parity wallet library contract into a regular multi-signature wallet by calling initWalletfunction.
The significant security vulnerability happened when a user accidentally swabbed the library code which contains the logic for multi-signature contracts on November 6, but Parity claimed that no coins were lost or stolen.
A similar thing happened in July when hackers harnessed a vulnerability and stole $30M worth of ETH. Parity refined the wallet. However, it either failed to notice or shirked the complication.