The top U.S. securities regulator said government lawyers are trying to determine if Wednesday’s big trading blunder at Knight Capital Group violated a new rule designed to protect the markets from rogue algorithmic computer trading programs.

The Securities and Exchange Commission’s market access rule, which took effect last year, requires brokers to put in place risk control systems to prevent the execution of erroneous trades or orders that exceed pre-set credit or capital thresholds.

The rule gets at the heart of what went wrong on Wednesday at Knight, after a software error led the brokerage to flood the market with erroneous orders over the course of 45 minutes.

Read More: Chicagotribune