Computer gremlins with zombie-like powers called botnets continue to spread through financial services systems, increasingly targeting smaller banks and credit unions, a new study says.

The problem is widespread in the business world. From January to April of this year, there were roughly 3.2 billion attacks each month on all industries by botnets — malicious code that spreads through a network of devices to surreptitiously act in unison, shooting out spam or conducting massive numbers of login attempts, according to the study conducted by the digital security firm Akamai.

Attacks spiked in May and June to 8.3 billion combined, the study said.

A popular tactic is to take stolen login information and use botnets en masse to key in this information at various websites, an act called “credential stuffing.”

Read more in American Banker.