As for OK.RU, it seems you might be referring to the Russian social networking platform OK.RU (also known as Odnoklassniki), where the movie might be available to stream or download.
If you type "piranha 3d ok.ru" into a search engine, you won’t have to dig deep. The top results will usually be direct links to the video page on ok.ru. Here is what you can expect: piranha 3d ok.ru