It usually means you could be on a scam site, not the site you think your on. For example, if you clicked a link to go to Android forums (this site) make sure the address bar says "androidforums.com/"
A few examples of possible scam sites could be:
"androidforum.com", an internationally misspelled name to try to trick you. Notice that the real forum has an 's' on the end
"androidforums.scamsite.com", it says androidforums, but its a sub-site of a different site, also designed to trick you.