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Thousands of websites across the globe were coming back online Tuesday after getting hit by a massive internet outage linked to U.S.-based cloud company Fastly.

High-traffic sites including Amazon, CNN, PayPal and the New York Times were down for as long as one hour earlier in the day, according Downdetector.com.

Fastly is one of the world's most widely-used cloud-based content delivery network providers – or CDNs – which help websites use less-congested routes, enabling them to move content to consumers faster.

Other CDN providers include Amazon’s AWS and Akamai Technologies.

Fastly reported a disruption from a (quote) "service configuration" but did not explain further.

Users received error messages when they visited the affected sites, which cyber experts say is an indication that Fastly was not a victim of a cyber-attack.

Reddit, Spotify and Bloomberg News were also down, as was the UK government’s website.

One media firm estimated that websites worldwide lost over $29 million in digital ad revenue per hour during the outage.