A rather significant bug has been spotted in Monero’s decoy selection algorithm that may impact your transaction’s privacy.

If users spend funds immediately following the lock time in the first 2 blocks allowable by consensus rules (~20 minutes after receiving funds), then there is a good probability that the output can be identified as the true spend.

This does not reveal anything about addresses or transaction amounts. Funds are never at risk of being stolen. This bug persists in the official wallet code today.

Users can substantially mitigate the risk to their privacy by waiting 1 hour or longer before spending their newly-received Monero, until a fix can be added in a future wallet software update. A full network upgrade (hard fork) is not required to address this bug.

The Monero Research Lab and Monero developers take this matter very seriously. We will provide an update when wallet fixes are available.

“This likely would only affect a tiny fraction of XMR transactions. The absolute maximum number of rings affected is probably <1% (since block 2300000, only ~1% of outputs used in rings were between 10 and 12 blocks old, and a percentage of those were likely decoys).”

Thus, all else equal, it would be next to impossible for this bug to compromise other transactions on the network (1% ^ 10 = 0.000000000000000001%).

Common sense principles:  This bug does not affect those who HODL their coins. Props to MRL for looking into possible fixes to this.  Bug free software doesn’t exist. Kudos to the people who found this bug and who are fixing it, that’s what keeps the coin great!

This really is just taking advantage of human behavior, the only way to fix this “bug” is to add pseudo human behavior to decoys, or time align all transfers.

Community response:  So the transactions of the best privacy coin were not private at all this is not a good thing, I trusted Monero.  Just after all the yanks bought up XMR to hide their crypto trading during the Bull Run so as to evade tax.  IRS tax professionals now have their heart’s content.

This shows that a longer track record is needed; there comes Bitcoin. This also shows that other privacy coins might be better than Monero. However, for most, I’d argue bitcoin from p2p exchanges + Coinjoin is good enough.

Some were like the same thing will happen to Zcash and every other privacy coin.