A criminal organization rented a lot of lyra2 hash capacity. Using this hash power, they double spended Vertcoin. On the Bittrex exchange, the criminals was able to withdraw money. The criminals mined in secret, owning more than 51% of the hash power. This made possible to execute the double spending attack. Monacoin also uses a variation of lyra2 algorithm, therefore, i recommend mona users to be more carefull for a few days.