The CentOS Project announced that updates for their CentOS 4 distribution will be discontinued on February 29th, 2012

This is the 6-month notification for the End of Life for the CentOS 4
distribution. The upstream provider will discontinue public updates of
their EL4 product on February 29th, 2012. The CentOS Project will end
support for CentOS 4 on the same date.

CentOS 4, as well as all previously released versions of CentOS, will
continue to be available in the Centos Vault:

http://vault.centos.org/

This CESA includes a new centos-release file that reminds you of the
February 29th, 2012 end of life date.

Users still running production workloads on CentOS 4 are advised to
begin planning the upgrade to CentOS 5 or CentOS 6 before the EOL date.

For users who are unable to migrate off the EL 4 code base before its
end-of-life date, the upstream provider intends to offer a limited,
optional extension program. The CentOS Project recommends that you
contact their sales team for a price quote for their extended service if
you can not move to a newer code base before February 29th, 2012.