Double spend is when a set of coins is spent in more than one transaction. This can happen for various reasons, but one of the reasons is fraud attempts
If you are accepting 0-conf payments, it's in your interest to detect double spend attempts. If you want merchants to accept your 0-conf payments, it's in your interest to help detect double spend attempts.
Bitcoin Unlimited detects double spends relayed to it and then forwards them to other nodes, so they aslo can detect them.
Help gathering double spends here and detecting them network wide by running Bitcoin Unlimited
Below are double spend this node has seen. Tags are applied to some as analysis for cause or motivation of the double spend.
Last detected: 2019-11-20 19:37:15.660915