Code:

function OnSystemAccount(): Boolean;

const

cnMaxNameLen = 254;

var

sName: string;

dwNameLen: DWORD;

begin

dwNameLen := cnMaxNameLen - 1;

SetLength(sName, cnMaxNameLen);

GetUserName(PChar(sName), dwNameLen);

SetLength(sName, dwNameLen);

if UpperCase(Trim(sName)) = 'SYSTEM' then Result := True

else

   Result := False;

end;