cperl-mode delete kills region

[Ivanov Dmitry]

I am using cperl-mode on Emacs 23.1.1 Windows. Sometimes, when I select a 
region and press delete Emacs calls kill-region and stores the text, that I am 
deleting into the kill-ring. For example I have text:

my $cookie = new CGI::Cookie(-name=>'CGISESSID',-value=> $self->{session}->id);

If I select -name=>'CGISESSID' and then press <Del>, it will be put into the 
kill ring. While selecting all the line doesn't do it. How  can I get rid of 
this, so <Del> won't put anything into the kill ring?