Create tx_spent.md

csv/tx_spent.md

@@ -0,0 +1,12 @@
+# Spent and risky transaction outputs
+Monero's untraceability is based on the sampling of decoy inputs for each real transaction input.
+If a decoy input is a reference to an output which is known to be spent, it does not contribute to the size of the anonymity set of the real input.
+To prevent the sampling of spent outputs as decoys, the blackballing tool (released together with Monero v.0.12) can be used.
+
+Lists of outputs which should be avoided can be obtained by following the links (which will be added soon).
+
+* Provably spent: [Link](#TODO)
+* (Probably) spent on a forked chain: [Link](#TODO)
+* At risk of being identified as spent: [Link](#TODO)
+
+These files cannot be included in the repo due to their size.