Now try to press ctrl-C twice in a row.

$SIG{'INT'} = sub {print "Caught One!\n"};
while(1) {
    sleep 1;
}
[download]

On ActivePerl 5.6.1/Win32, the program is exited the second time you press ctrl-C. Apparently the signal handler gets cleared... setting the signal handler again makes it work again. Of course, there will still be a short crack where it's still vulnerable.

On ActivePerl 5.8.3, it keeps working.