A group of researchers discovered that roughly 1,000 brain wallets have been drained by cyber criminals that have stolen $103,000. Brainwallet refers to the concept of storing Bitcoins in ones own mind by memorization of a passphrase. Experts identified 884 brain wallets storing 1,806 BTC (worth approximately $100,000) and discovered that only 21 of them were not drained. Researchers published a paper demonstrating the efficiency of their Bitcoin Key Recovery Attacks, that is 2.5 times faster compared to the method developed by Ryan Castellucci.”]
Source: https://securityaffairs.co/wordpress/44532/cyber-crime/103k-stolen-brain-wallets-attacks.html