The bank, which provides managed online banking services for more than 60 US organisations, put in protection systems last year after a series of attacks by spamming groups disrupted e-mail communications with its 8,000 banking customers.
Bancorp discovered its systems were being bombarded by messages from hacking groups attempting to identify valid e-mail addresses on the company's systems for resale to spammers.
Pete Chiccino, chief security officer at Bancorp, said, "This caused a slowdown in mail delivery because we were trying to process the invalid messages. It took us offline while we waded through 30,000 e-mails. One time it was an entire day."
Bancorp invested in two Tumbleweed Mailgate Edge mail relays, which can identify and filter out the attack messages before they reach Bancorp's systems, which are based on Windows, Unix and Linux.
"We are an internet-based business, so e-mail is our primary communication. When e-mail goes offline it is a huge hit. Since we have put in the Edge relays we have had no problems," said Chiccino.