Recently, the team behind Monero (XMR), the anonymous cryptocurrency that saw its price surge after darknet market AlphaBay started accepting it as a payment method, discovered a bug in CryptoNote-based currencies that allowed double-spending, meaning an infinite amount of coins could be created.
Thanks to the exploit, the coins were created in an undetectable way, unless the observer knew about the flaw and was able to search for it using specific code. Monero’s team quickly patched the bug as soon as it was discovered and stated that the anonymous currency’s blockchain wasn’t affected. The disclosure reads:
"We patched it quite some time ago, and confirmed that the Monero blockchain had NEVER been exploited using this, but until the hard fork that we had a few weeks ago we were unsure as to whether or not the entire network had updated."
Read more here: https://www.cryptocoinsnews.com/cryptonote-currency-bug-allowed-creation-unlimited-number-coins/