It is very easy (and free) to find out if your hub has been copied as you can use a service called copyscape. Got to www.copyscape.com and put the url of your Hub - or any web page you want to check, into the box.
Copyscape will then search the web, not only for exact copies but for articles that might reproduce chunks of your work in a way that is beyond the realms of chance (reproducing popular short phrases, etc.).
Of course, you might find when you check the website where copying seems to have occurred, that this is a legitimate 'syndication' of part of your article which gives proper credit to the source by providing a link back to your hub and this is the best kind of backlink you could possibly have (provided it is from a reputable site, of course) as this is natural 'organic' link-building which Google is looking for when ranking sites and individual web pages.
Finding a version of your article that has been 'spun' to pass copyscape and published on another site is very much more difficult. The saying "there is nothing new under the sun" is particularly true on the Internet. Content is recycled and repurposed all the time. There is a whole army of web-content writers who get paid a few dollars an article to provide 'fillers' for other people's web sites. They trawl the net, looking for a good article on a topic and Hubpages is a great source for them. The quickest way for them to produce a good article for sale is to rewrite an even better article (or a large section of it), get it to pass copyscape and 'bingo' - another saleable article.
Google and other search engines are getting cleverer at spotting this type of content though and I believe that a time will come when a big percentage of it will get weeded out and will never get indexed - or will get de-indexed pretty quickly.
Plagiarism is always going to be a problem but if you are the writer of a top quality hub, you will get your article indexed first and you will get the credit for it if you publish on a high ranking site like Hubpages.