The LockWorkStation function locks the workstation’s display,
protecting it from unauthorized use.
This function has the same result as pressing Ctrl+Alt+Del and
clicking Lock Workstation.
To unlock the workstation, the user must log in.

Windows NT/2000/XP: Included in Windows 2000 and later.
Windows 95/98/Me: Unsupported.

procedure TForm1.Button1Click(Sender: TObject);
begin
  LockWorkStation;
end;

{ Loading LockWorkStation dynamically}

function LockWS: Boolean;
// by Thomas Stutz, SDC
type
  TLockWorkStation = function: Boolean;
var
  hUser32: HMODULE;
  LockWorkStation: TLockWorkStation;
begin
  // Here we import the function from USER32.DLL
  hUser32 := GetModuleHandle('USER32.DLL');
  if hUser32 <> 0 then
  begin
    @LockWorkStation := GetProcAddress(hUser32, 'LockWorkStation');
    if @LockWorkStation <> nil then
    begin
      LockWorkStation;
      Result := True;
    end;
  end;
end;