Jim Rohr says cybersecurity is one of the biggest issues banks face.

The frequent distributed denial-of-service-attacks on banks' web servers that have occurred since September are doing more than disrupting service. "All this is test-and-learn," he says, and defenses must be strengthened before the bad guys learn enough to do some serious harm.

The PNC bank CEO shared this perspective in an interview with American Banker Editor at Large Barbara A. Rehm.

Rohr, who stepped down last week after running PNC Financial Group for 13 years but will stay on for a year as the bank's executive chairman, told Rehm he worries that some financial institutions don't have the resources or sophistication to defend themselves from hackers.

"One of the things that concerns me is they are going to go in and take over the identity of a small bank," he says, and then use that entry point to get inside the larger firms. "One of the questions we need to ask ourselves — and this won't be popular — but are you too small to defend yourself"