A famous Australian SEO Dan Petrovic of Dejan SEO has proven with a series of experiments that is now possible to hijack Google Search Result by simply duplicating a target page on your own domain and +1-ining it on Google+.
You can learn more about the process here.
While Search Engine Land reported on the story, some interesting comments were posted over there. Seems like black-hat SEOs have picked up the story and are already using the technique for several highly competitive keywords on google.co.uk.
Let’s hope Google puts some extra measures in place to protect us.