[JJR512]

Without knowing which exact version you have, I couldn't really tell you what the difference is...you can find which version you have in the instructions.txt file, there's a version history at the top. That also tells you what the differences are.

Basically, the C and D releases are fine (D is just fixes a poorly-written instruction as pointed out by Mystics). In all the earlier versions, a thread would get closed even if someone who had checked the box just hit the Preview button, and this might not be desirable operation. In the original version, there was also a small security hole that could allow anyone to close any thread if they knew how to manipulate forms data and tried it. Functionally, every version has done the basic idea of what this hack is, but I would use at least version C.