Stock exchange systems must focus on security, resiliency: Greifeld

Stock exchange systems have thus for focused on functionality, user-friendliness and speed, but the next generation must tackle security and resiliency, Nasdaq CEO Robert Greifeld said Friday.

Greifeld made his comments two days after its rival, the New York Stock Exchange, halted trading for nearly four hours following "unusual system behavior" resulting from a problem connected to a software update.

"When something goes wrong the system has to continue to run," he told CNBC's "Squawk on the Street." "The good news is computer technology has come along where we can do many things today on both cybersecurity and resiliency that was not available to us five years ago."

Read MoreCramer: NYSE halt shows its lost importance

The Nasdaq suffered its own hourslong outage in 2013 due to an internal software bug and connection problems with its system and NYSE's Arca.

While both outages were caused by internal errors, Greifeld said exchanges should be equally concerned with security and resiliency.

"We spend a lot of time on cybersecurity, and we know the threat vectors change really on a daily, monthly basis, so we could be good enough today, but not nearly good enough tomorrow," he said.

"With respect to resiliency of the system, we have to get very good at testing the negative case," he added, saying exchanges are proficient at testing whether a system will work.

Greifeld said the NYSE is "very capably led" by Intercontinental Exchange founder, CEO and Chairman Jeffrey Sprecher and NYSE Group President Tom Farley, but the executive team is dealing with legacy issues from previous administrations.