24 April 2019 Update
We found the root cause of the irregular Zerocoin spends on the 19 April 2019. An emergency update 13.7.9 is now available to disable Zerocoin completely while we move to our Sigma implementation. We are in touch with a number of other Zerocoin projects and are working together to secure it.
We recommend any projects utilizing Zerocoin (regardless of which implementation you are using) to disable Zerocoin on sporks or at a consensus layer.
A disclosure with the root cause of the fix will be released once we are satisfied that there is no longer any threat.
On 9 April 2019, the Zcoin team uncovered irregularities in connection with an isolated number of Zerocoin spends.
Zcoin immediately contacted pools to disable Zerocoin spends and are investigating the issue. This means that minted coins cannot be spent until further notice but will be spendable once the issue is resolved. No user funds are at risk.
We have informed other projects using the Zerocoin protocol and are working with them to address the issue. Further details will follow once fully addressed by affected projects.
Zcoin has also been working to implement the Sigma protocol to replace Zerocoin. Sigma will be launched on our testnet soon. More details can be found in our article “What is Sigma and why is it replacing Zerocoin in Zcoin?“.