Nelson runs what is known as the Financial Services Information Sharing and Analysis Center, or FS-ISAC, which is based in Northern Virginia.
It's a private sector effort to cooperate and effectively crowdsource solutions to cyberattacks as they happen. Member banks—and all the biggest banks are members—share details of attacks as they come in, including things like IP addresses of attacking computers or the subject lines of phishing emails. That allows the others to search their own systems for evidence of the same attack, or share ideas on how to root it out.
Read MoreNorth Korean cyberattack may cost Sony millions
"We see thousands of attacks against financial services every day," Nelson told CNBC on Thursday, in the first TV interview from inside the FS-ISAC. "Some of them are just probes and scans," he said. "Some of them are cyberattacks by cybercriminals. Others can be nation-state attacks looking for intellectual property. But it's a really growing problem."
The FS-ISAC is owned by its members, and was created in 1999. Today, staffers there use a critical infrastructure notification system to send alerts of attacks in progress to member firms around the world. (Check out this map of cyberattacks in progress.)
It is a private sector effort, but Nelson and his team work closely with the U.S. government, passing along details of threats spotted by the U.S. Secret Service and the U.S. intelligence community.
Read MoreInside North Korea's scrappy, masterful cyberstrategy
Asked directly if what happened to Sony could happen to the banks, Nelson didn't specifically answer the question. Instead, he said: "We've been under attack for years in the financial services industry. I include banks, insurance companies, stock exchanges. And integrity of the payments system and the settlements system is very important."