The Secret Service need not disclose recent logs of White House visitors since it would effectively reveal the president's calendar, the D.C. Circuit ruled.
Through its White House Access Control System (WHACS), the Secret Service keeps a record of every person's entrance and exit into the White House complex, which includes the White House, the Eisenhower Executive Office Building, the surrounding grounds and the New Executive Office Building.
Source: Courthouse News. Read full article. (link)