How to correct his error?

Hello,
  g++ v4.8.1
  linux 3.11.10-11-desktop x86_64

  I am trying to compile an old program (from 14 years ago) with my own
equally rusty knowledge of C++. I am stuck on this one error: I have no
idea what "looser throw specifier" means.

The code:
class SimpleException : public exception
{
    public:
        string what;
        SimpleException(const string & _what) { what = _what; };
};

The error:
$ make
$ g++ -Wall -I. -DLIBIMAP_DEBUG -D_REENTRANT_ -DREENTRANT -c libimap.cpp
-o libimap.o
In file included from libimap.cpp:26:0:
libimap.h:111:7: error: looser throw specifier for ?virtual
SimpleException::~SimpleException()?
 class SimpleException : public exception
       ^
In file included from /usr/include/c++/4.8/ios:39:0,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from libimap.h:26,
                 from libimap.cpp:26:
/usr/include/c++/4.8/exception:64:13: error: overriding ?virtual
std::exception::~exception() throw ()?
     virtual ~exception() _GLIBCXX_USE_NOEXCEPT;
             ^
make: *** [libimap.o] Error 1

--
James Moe
jmm-list at sohnen-moe dot com