Shylock is what is known as a "Trojan" and is downloaded by unsuspecting internet users clicking on malicious links on websites usually set up by the fraudsters. It targets computers running Microsoft Windows, and when infected, criminals can take control of a computer and potentially use it to access online bank accounts.
Following action by a number of law enforcement agencies including the UK's NCA, the criminals' ability to take control of computers and carry out fraud has been severely damaged.