There have been nine versions of Visual Basic up to the current version. The first six versions were all called Visual Basic. But in 2002, Microsoft introduced Visual Basic .NET 1.0, a completely redesigned and rewritten version that was a key part of a whole computer software revolution at Microsoft. The first six versions were all "backward compatible" which means that later versions of VB could handle programs written with an earlier version. Because the .NET architecture was such a radical change, any programs written in Visual Basic 6 or earlier had to be rewritten before they could be used with .NET. It was a controversial move at the time, but VB.NET has now proven to be a great programming advance.
One of the biggest changes in VB.NET was the use of a object oriented software architecture (OOP). (Tutorials on the site explain OOP in much more detail.) VB6 was 'mostly' OOP, but VB.NET is totally OOP. The rules of object orientation are recognized as a superior design. Visual Basic had to change or it would have become obsolete.