You can come to a same page with the same or similar content with many different urls. Query strings may have user id, session id, and many more. All these varied urls work unfavourably toward SEO. It will be best to clean up your urls, but there is a easy and quick way to get around it. It is canonical link.
It's supported not only by google, but by microsoft and yahoo as well. (http://searchengineland.com/canonical-tag-16537)
Recently, I added a 1 x 1 px hidden iframe on the site home for tagging purpose. The page that is loaded within the iframe does not need to be indexed and the url is better not to be kept in search engine. So what I did is
<meta name="robots" Content="noindex">
<link rel="canonical" href="https://www.sitehome.com" />