"Cyberattacks on our financial system represent a real threat to our economic and national security," Lew said in prepared remarks. "But a malicious cyber actor can cause catastrophic damage to our financial system without directly attacking a bank."
He called for Congress to pass regulations to address the myriad aspects of cybersecurity.
"As it stands, our laws do not do enough to foster information sharing and defend the public from digital threats," Lew said. "We need legislation with clear rules to encourage collaboration and provide important liability protection. ... And we need legislation that protects individual privacy and civil liberties, which are so essential to making the United States a free and open society."
This marks the second appearance of Lew, who spoke at Delivering Alpha in 2013 just a few months after being confirmed as the first post-financial crisis Treasury secretary.
The remarks come as several companies have experienced high-profile data breaches.
In a similar vein, he said companies that come under threat on social media, such as from false statements on Twitter and other sites, need to act quickly when that happens.
—By CNBC's Jeff Cox