A glitch forced the New York Stock Exchange to halt trading for nearly four hours Wednesday, an outage that unnerved Wall Street and revived concerns about the fragility of the technological systems that underpin financial markets.

It was the longest technology-related disruption at the NYSE in recent memory and a black eye for Big Board owner Intercontinental Exchange Inc. Industry watchers said it is likely to draw more regulatory scrutiny of the exchange operator, which has sought to trim costs since buying the NYSE in...