ION’s Derivatives System Hack Sparks Caution in Equities Market

A cyberattack in a little-known corner of the derivatives market has Wall Street’s biggest trading desks treading carefully in other markets unscathed by the incident, a sign of jitters pulsing through an industry on watch for such attacks.

Banks including Citigroup Inc., Bank of America Corp. and Morgan Stanley are carefully reviewing trades sent through systems operated by ION Trading UK, which announced this week that a software business that underpins cleared derivatives markets globally was under attack. Those moves, described by people familiar with the matter, signal how cautious banks are being even in unaffected markets such ...