A botched software update at Spain’s central domain registry knocked as many as 400,000 sites offline for several hours Tuesday, according to the Esnic registry. The error left Internet users unable to access domains using .es, the country code top-level domain for Spain. The outage lasted from 3 pm to 5 pm Tuesday afternoon (local time) when the DNS database that connects domain names to IP addresses was “affected by an error” during a software update, according to an advisory posted at Esnic, which manages the .es database.

The outage can be clearly seen in our performance chart for Arsys, the largest hosting company in Spain, which uses Arsys.es as its primary domain. Arsys hosts more than 600,000 hostnames, although only some of those use .es for their domain. Other top-level domains were not affected.

Netcraft offers a web site performance monitoring service that provides detailed uptime charts, along with e-mail alerts when an outage occurs.