witter messages are public, but users can also send private messages.[222] Information about who has chosen to follow an account and who a user has chosen to follow is also public, though accounts can be changed to "protected" which limits this information (and all tweets) to approved followers.[223] Twitter collects personally identifiable information about its users and shares it with third parties as specified in its privacy policy. The service also reserves the right to sell this information as an asset if the company changes hands.[224] While Twitter displays no advertising, advertisers can target users based on their history of tweets and may quote tweets in ads[225] directed specifically to the user.