In versions 7.81 and higher:

In Administration, specify the appropriate rights for accessing Personal Information.

In versions 7.80 and prior:

  1. In Administration, click Security 
  2. Open the appropriate security group
  3. Highlight Records and click Options
  4. Under Miscellaneous Constituents Options, unmark the Social Security Number checkbox to prevent users from viewing the field or mark it to allow them to view the field