The websites of HSBC, ITV and Waitrose were part of a widespread outage that briefly caused disruption on Thursday afternoon.
Major online banking services, including Barclays, TSB, Bank of Scotland, Tesco Bank and Sainsbury’s Bank, have been totally or partially inaccessible for a short time.
Airbnb, PlayStation Network, and Steam also encountered the temporary issue, with some showing users a DNS error.
Unconfirmed reports suggest the issue may be related to a performance product offered by Akamai, a US company that began investigating the issues just after 5 p.m. UK time.
Its Edge DNS service is designed to improve load times and combat attacks, using a network of servers spread around the world.
Akamai later tweeted, “We have implemented a fix for this issue, and based on current observations, the service is resuming normal operations.
“We continue to monitor the situation and can confirm that this is not a cyber attack on the Akamai platform. “
The incident follows a similar outage six weeks ago, which impacted major websites, including gov.uk offline.
US company Fastly said the issues on June 8 were due to an “undiscovered software bug” in its system that was triggered by a single anonymous customer who updated their settings.