The London Stock Exchange denies that a cyber attack was responsible for a trading outage in August. U.K. security agencies are reportedly investigating the cause of the incident.

According to a news report, the incident delayed the market opening by more than an hour and a half and is the London index’s worst outage for eight years. The Wall Street Journal reported that the outage immediately triggered government cyber alert systems, and GCHQ is examining whether the software code could have played a role in the incident. 

In addition, the news report notes that a spokesperson for the London Stock Exchange Group (LSEG) denied the incident was related to cybersecurity and said it “was caused by a technical software configuration issue following an upgrade of functionality." The status of the investigation and whether any action will be taken by regulators or the LSE is not clear.

A spokesperson for the National Cyber Security Centre said, “the NCSC has not treated the LSE outage as a cyber security related incident and has not investigated it as such.”