.cer

Security file provided by a third party such as VeriSign or Thwate that confirms the authenticity of a Web site; installed on a Web server (such as Apache or Windows Advanced Server) to authenticate the validity of a certain website hosted on the server; represented by a lock icon near the edge of a browser window when accessing a secure site (beginning with "https://").

The information from a secure certificate can be viewed by double-clicking the lock icon located near the bottom of a browser window in Internet Explorer or Firefox; to view the certificate information in Safari, click the lock icon near the top-right corner of a browser window.