There seems to be a vulnerability in Parity Multisig wallets version 1.5 and higher. A White Hat group is sweeping affected wallets right now to contain the damage but $30M may have already fallen in the hands of the Black Hat group.
Developing....
Sources: https://www.reddit.com/r/ethereum/comments/6obofq/a_modified_version_of_a_common_multisig_had_a/
https://press.swarm.city/parity-multisig-wallet-exploit-hits-swarm-city-funds-statement-by-the-swarm-city-core-team-d1f3929b4e4e
