Several major websites went out briefly on Thursday due to a widespread outage associated with the Akamai content distribution network.

At around 12:50 p.m. ET, Akamai said the issue had been fixed and service appeared to be back to normal. The company later announced on Twitter that the problem was caused by a software update that triggered a bug. It confirmed that the incident was not the result of a cyber attack on its platform. Akamai said the disruption lasted “up to an hour” and apologized for the inconvenience.

Akamai, whose operation helps transmit data on the Internet, said on its website Thursday that it is investigating “an emerging problem with the Edge DNS service.”

Oracle had also pointed to Akamai as the cause of the problem, which affected some Oracle Cloud properties, but resources within its own cloud service were not affected.

The Domain Name System is like a phone book for websites. The technology determines the correct IP addresses to use when users try to visit individual websites. Akamai’s Edge DNS service does this work for apps and websites, protecting against distributed denial of service or DDoS attacks.

Delta Air Lines, British Airways, Capital One, Go Daddy, Vanguard, UPS, LastPass, AT&T, and Costco were among the sites that were loading slowly or displaying “DNS Errors” on Thursday afternoon.

The failure caused some glitches in the real world. For example, Delta customers could not use the airline’s website or app to check in flights until Akamai corrected the problem.

– CNBC’s Leslie Josephs and Jordan Novet contributed to this report.