When soapUI generates the WS-Security headers for a soap message it does not provide a way to add a <wsse:Nonce> tag. For services that check replay attacks, like .net, need the nonce to be filled in.
As such, this needs to be generated when a wsse header is created.
A nonce is a randomly generated number that is added to the message. The hash is created from the creation time and the nonce. Since the nonce is never repeated, a service can remember the nonce to foil replay attacks where the same message is sent a second time.