This is a very important question. There certainly is a proliferation of information, even private information. In fact, with the advent of the Internet, there has been an acceleration of information. In light of this, companies must try their best to protect the privacy of people. They are successful in varying degrees.
There are several ways that companies seek to protect people. Let me list a few ways.
First, all online information is encrypted. The reason for this is to prohibit any hackers from gaining access to personal information. Second, some companies have set up passwords and pin numbers for people to access their accounts, whether it is online or over the phone.
Third, there are also sophisticated algorithims to monitor unusual spending, at least in the case of credit cards. When this happens, the credit card may be frozen or a phone call may be given to verify spending and indentity. Fourth, there are many third party companies that track your personal information to see if it has been compromised in any way. These companies, of course, charge a fee, but they can be effective.