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function IsWorkstationLocked: Boolean;
var
  hDesktop: HDESK;
begin
  Result := False;
  hDesktop := OpenDesktop('default',
    0, False,
    DESKTOP_SWITCHDESKTOP);
  if hDesktop <> 0 then
  begin
    Result := not SwitchDesktop(hDesktop);
    CloseDesktop(hDesktop);
  end;
end;                    

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function IsLocked : boolean;
var
  Desk : HDESK;
  Name : Array[0..4095] of AnsiChar;
  len : Cardinal;
begin
  result := true;
  Desk := OpenInputDesktop(0, false, DESKTOP_SWITCHDESKTOP);
  if Desk = 0 then
    exit;

  len := sizeof(Name);
  if not GetUserObjectInformationA(Desk, UOI_NAME, @Name, len, len) then
    exit;

  if (CompareText(Name,'Winlogon') = 0) or
    (CompareText(Name,'Disconnect') = 0) or
    (CompareText(Name,'Screen-Saver') = 0) then
    result := true
  else
    result := false;
end;