VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL).
Oracle released VirtualBox 3.1.8, a maintenance release of VirtualBox 3.1 which improves stability and fixes regressions.
You can check what is changed on this version from here
Download virtualbox 3.1.8 for ubuntu 10.04/9.10/9.04/8.10/8.04 from here
Install .deb packages using the following command from your terminal
sudo dpkg -i virtualbox-3.1_3.1.8-61349~Ubuntu~lucid_i386.deb