A zero-day vulnerability is suspected of causing BIND 9 DNS server crashes across the web.
BIND 9 is the most widely used DNS server on the internet, meaning the flaw could have a massive impact.
"Organisations across the internet reported crashes interrupting service on BIND 9 nameservers performing recursive queries... An as-yet unidentified network event caused BIND 9 resolvers to cache an invalid record, subsequent queries for which could crash the resolvers with an assertion failure," the Internet Systems Consortium (ISC) said in an advisory.
"ISC is working on determining the ultimate cause by which a record with this particular inconsistency is cached."
ISC, which manages the BIND software, has issued patches to prevent servers from crashing.
"At this time we are making available a patch which makes named recover gracefully from the inconsistency, preventing the abnormal exit," it added.
Security intelligence firm Rapid7 said the first attack was discovered at the US National Weather Service and at US universities.
"Bind 9 is the most widely used DNS server on the internet today… Gone unchecked, this attack could potentially affect nearly the entire internet," said Matt Barrett, senior solutions architect at Rapid7.
"A temporary patch has already been released, but we encourage everyone to submit packet-capture from their own systems to ISC so they can further investigate. As with any attack, the more information gathered, the better we’ll be."