This is meant to keep version for your class so that it won't try to deserialize objects having incompatible versions. otherwise it will throw InvalidClassExceptions for incompatible versions.
That actually means that you are using an IDE where you have set an option to include an “default” SUID number in every Serializable class. I think you should take that option off.
Look here, where you will find links to discussion of serialisation, which will help explain what an SUID is.