ATTENTION! Users of "Generation 3" browsers (Netscape 3.x, MSIE 3.x, Mac IE.4.x) will need to update their root certificates. Please click here for instructions. It is a two minute process and it is important that you do this!
Additional information is available here and at the Thawte website here. This eventually affects all certificate authorities (CA's), including Thawte, Verisign, etc.