Companies can only log information about your interaction with their sites. With very few exceptions, that just means on whatevercompany.com. Basically, they on

Companies can only log information about your interaction with their sites. With very few exceptions, that just means on whatevercompany.com. Basically, they only have the data you explicitly give them. In the case of some large sites that provide pervasive services like FB, Twitter, and Google, you interact with their sites incidentally as you surf in the internet. It's these sites that are a potential privacy risk IMO.