TwitViewer is a malicious tool that pretends to show you who the latest people were who viewed your Twitter profile. TwitViewer does not provide this functionality, because Twitter doesn't make this information available. TwitViewer instead steals your Twitter credentials and immediately sends a tweet on your behalf, linking back to TwitViewer. If you've already provided your Twitter credentials to TwitViewer, change your Twitter password immediately.
Used TwitViewer? Updated your Password Immediately