Pinning Software Packages in Ubuntu
Ubuntu has an excellent package management system and this page describes how to prevent upgrades of specific packages.
Ubuntu uses Debian packages for it's package management. For the most part the packages supplied by Ubuntu are very usable. But in the rare instances that you need to rebuild a package to enable an option (mysql) you might need to prevent a specific package from updating automatically. This procedure is also known as pinning the package. To pin the "vnc4server" package create a file called "preferences" in /etc/apt and add the following:
Package: vnc4server
Pin: origin ""
Pin-Priority: 999
The next time you "apt-get upgrade" you won't be alerted to changes in the vnc4server package.
Note: this means that you must manage security patches to this package manually.