Wikipedia is an example of a website filled with useful facts, easy to use, first site which appears on Google, but still have flaws in some articles because people can easily edit it without any form for approval. Students are being advised against using Wikipedia, but still we use, because finding an article on Wikipedia about pretty much anything is so easy. By doing this, we lose the skills to find other more reliable sites, and therefore keep using Wikipedia.The best way to find good, correct facts is to find sources you know are reliable, like articles written by experts, teachers or other qualified people. Another encyclopedia (not Wikipedia) you know is written by professionals might be a good source. Controlling your facts by crosschecking them with other sites is a good way to find out whether the facts are true or not, but of course this requires more work.
So using internet during an exam can help you a lot in form of providing information, just make sure you fin reliable sources, or at least double-check you facts trough several websites.