This will continue and be a big problem. I suspect this has happened frequently already but the events are covered up by the companies.
At one time, when banks and other institutions were smaller, most employees were very loyal. Generally the jobs were very secure and pleasant.
However, today banks have shifted from a family atmosphere to a boiler room. Employees now work in high pressure call centers where every keystroke is monitored and EVERY error counted. Calls are timed. There are strict quotas to be met. These are the equivalent of the old Ford high speed assembly line, only electronic instead of mechanical. Employees are just a "resource", nothing more. They come and they go and no one cares.
Such atmospheres are more conducive to bad behavior, sabotage out of spite, etc.
I remember a "Wonder Years" where Kevin got a job working at an old fashioned hardware store. The owner was a grouchy old man. But Kevin learned the hardware business well and the owner's wife treated him like a son. Kevin left and became an anoymous mall rat, not staying very long at a food stand, and no one caring.
Those small businesses and that kind of boss-worker relationship are very rare today with almost everything run by chains. "Managers" are some young self righteous snit, probably someone who was in the corridor patrol in high school and took pleasure in challenging kids for their hallpasses and kicking out those who didn't have them. The owning corporation looks at some numbers, not at people, despite what their house newsletters and commercials proclaim.
Again, these are the atmosphere where employees feel like no one cares -- because no one cares -- and more likely to lash out from the mindless bureacracy and quotas shoved at them. People who lash out steal. What's to stop some bored waiter from taking a friend's black box and secretly reading credit cards presented for payment?