The SharePoint December 2009 Cumulative Update was released on December 15, 2009, it consists of two particular updates WSS 3.0 – KB 977027 and MOSS 2007 – KB 977026.
Once the updates are applied the new version is: “12.0.0.6524”, as always make sure you backup properly your Farm in case of any possible disaster.
In case you are interested in finding in more details about the current SharePoint Level the following links are very useful: