I suggesting asking over on the
Google Chrome Help Forum. They're better at answering user questions as this list is for Chrome App developers and our answers will likely be very technical and hard to follow.
Chrome Apps and Extensions shouldn't appear unexpectedly. They must be installed by visiting the Chrome Web Store and clicking the "install" button. Installing things without your approval is a common malware technique. If you put chrome://extensions in your address bar you can see all the apps and extensions you have installed and remove any your don't remember installing.
If you mean that you suddenly have a "Chromium" app installed, when you expect to have "Google Chrome" this may mean that malware has replaced Chrome with an infected version of Chromium, the open source project Chrome is based on. If you put chrome://chrome in your address bar it should say "Google Chrome" and have a red, green and yellow logo. If it says "Chromium" and has a blue logo then your browser has been replaced.