Ubuntu announced the end of life for Ubuntu 10.04 "Lucid Lynx" on April 30 2015 -- they will be providing no more updates for this Ubuntu version.
Support for Virtualmin on Ubuntu 10.04 will be ending as well. There will be no more releases for this Ubuntu version; we recommend that users of Ubuntu 10.04 either migrate to a newer distribution, or perform an in-place upgrade to 12.04 or 14.04, both of which have active support.
You can read the official Ubuntu 10.04 End of Life announcement here:
http://fridge.ubuntu.com/2015/03/18/ubuntu-10-04-lucid-lynx-reaches-end-...
Documentation regarding how to upgrade from Ubuntu 10.04 to 12.04 is available here:
https://www.virtualmin.com/documentation/system/os/ubuntu-lucid-to-precise