A study conducted by the NSA confirms that telephone metadata from phone logs reveals individuals Personal Information to government surveillance agencies. The researchers gathered metadata on more than 250,000 calls and over 1.2m texts. Given just one phone number to start with, the NSA program would have access to telephone metadata for tens of millions of people. With restrictions in place, however, the number plummetsbut still indicates that armed with just a phone number, it is possible to retrieve metadata on 25,000 people.”]
Source: https://securityaffairs.co/wordpress/47492/intelligence/nsa-telephone-metadata.html