Law firms often have accounting departments with access to wire transfer capabilities through online banking. There is a risk with these systems of infection with malware (i.e. keyloggers) and then unauthorized wire transfers of hundreds of thousands of dollars. A Toronto firm in 2012 had a "six figure loss" from this type of attack. These attacks are likely just the tip of the iceberg because law firms don't like to admit to having had trust funds stolen.
A good solution to the problem of attacks on accounting computers is to air gap them. The strategy is to provide a dedicated computer with a separate internet connection for wire transfers. Having a separate computer (and internet) means that any infections on the network or in an email attachments can't affect the banking computer. This method would have prevented the two attacks linked to above (and virtually any other kind of attack).