UK internet registry Nominet has signed the .co.uk second level domain with the DNSSEC protocol.
DNSSEC allows security to be embedded in the internet, and prevents URL spoofing, and other attacks.
Nominet said on Thursday that it had rolled out DNSSEC for .co.uk on Tuesday 3 May.
"The signing of .co.uk was an important step in securing the .uk zone and continues the deployment of DNSSEC across all .uk zones managed by Nominet," said the company in a statement.
All second level .uk domains will be signed by 18 May, Nominet added.
DNSSEC relies on a chain of trust within the DNS infrastructure, from root servers through to individual zones. Icann published the root zone anchor for DNSSEC in July 2010.