The official announcement on the SharePoint team blog can be found here.
The WSS V3.0 hotfix KB956057 article can be found here: http://support.microsoft.com/kb/956057
The SharePoint 2007 hotfix KB956056 article can be found here: http://support.microsoft.com/kb/956056/
The important thing to note is that we will be releasing cumulative updates every two months to ensure an ongoing quality product for our customers.
I would recommend you test these fixes in your test/staging environments prior to implementing these into your production environment. These hotfixes are updates to the infrastructure updates that were released in July.