Because Websecurify is quite dynamic runtime, you should expect to see new releases quite often (pretty much every month or so). Some of these releases have special versioning and meaning which I would like to walk you through.
First of all, every single websecurify version contains a number which specifies the milestone release it is part of. For example 0.2, 0.3, 0.4, etc are part of the Websecurify 1.0 milestone release. On the other hand 1.1, 1.2, ..., 1.9 are part of the Websecurify 2.0 milestone release.
Between these version we have loads of alpha, beta and RC releases. Alpha and Beta releases contain the keyword Alpha or Beta in the version string, followed by a sequential number, i.e. 0.5Alpha1, 0.5Beta1. You should expect to find a lot of bugs in these release and they are targeted to developers only.
RC releases, meaning Release Candidate, are versions of the product which are almost ready for primetime use. You should expect only a few bugs if any when you are trying a release candidate. RC versions are composed of the keyword RC followed by a sequential numbers just like the Alpha and Beta releases, i.e. 0.6RC1.
In order to simplify the testing stages, the Websecurify runtime is configured to use different naming conventions and to install in different places based on its version. For example 0.5 shall replace/upgrade the previous 0.4 release while 0.6RC1 will install an independent version. This means that developers and users can try out developing versions along side the stable version of the product.
So, do not hesitate to download the latest Alpha, Beta or RC release and give it a try. It is safe.