As has been reported, Umbra was used to move funds associated with recent, high profile hacks. In total, we are aware of 349 ETH (~$800K) of stolen funds moving through the protocol. Reports of much higher amounts are inaccurate. A few notes:
First, as a stealth address system, Umbra is primarily useful for protecting the identity of the receiver, not the sender. Since hackers want to erase the association of funds with the hack-tainted sending address, it is not particularly helpful to hackers to move the funds through Umbra. All the stolen funds moved through the protocol can be identified, and we have been in touch with security researchers who are involved.
Second, Umbra is a permissionless protocol powered by autonomous smart contracts. There is nothing we can do to stop anyone from using these contracts, nor is there anything we can do to stop anyone from using a local or self hosted version of the Umbra frontend, which is fully open source.
We did, however, make the decision to move our hosted version of the frontend into maintenance mode. We did so this morning at 6:45 AM ET.
Please note that all funds in stealth addresses are completely safe and were never at risk. The Umbra protocol continues to operate normally, we've simply turned off our instance of the frontend.
We will restore access to the hosted frontend as soon as we are assured that doing so won't create obstacles to the current recovery efforts.
Updates will be posted here.