Many people don’t think about the security implications of this information existing in the first place. They might be aware that it’s mined for advertising and other marketing purposes. They might even know that the government can get its hands on such data, with different levels of ease depending on the country. But it doesn’t generally occur to people that their personal information might be available to anyone who wants to look.
Source: The Security Risks of Third-Party Data – Schneier on Security