If you are wanting to see who is probing tcp/80 (http) then you could use IO::Socket and get the details of the client.
Google turned this up for me...
http://www.infocopter.com/perl_corner/socket-server.htm
#!/usr/bin/perl -w
# server0.pl
#--------------------
use strict;
use Socket;
# use port 7890 as default
#my $port = shift || 7890;
my $port = 80;
my $proto = getprotobyname('tcp');
my $logfile = "/tmp/logfile";
# create a socket, make it reusable
socket(SERVER, PF_INET, SOCK_STREAM, $proto) or die "socket: $!";
setsockopt(SERVER, SOL_SOCKET, SO_REUSEADDR, 1) or die "setsock: $!";
# grab a port on this machine
my $paddr = sockaddr_in($port, INADDR_ANY);
# bind to a port, then listen
bind(SERVER, $paddr) or die "bind: $!";
listen(SERVER, SOMAXCONN) or die "listen: $!";
print "SERVER started on port $port\n";
# accepting a connection
my $client_addr;
while ($client_addr = accept(CLIENT, SERVER)) {
# find out who connected
my ($client_port, $client_ip) = sockaddr_in($client_addr);
my $client_ipnum = inet_ntoa($client_ip);
my $client_host = gethostbyaddr($client_ip, AF_INET);
# print who has connected
open(OUT, ">$logfile");
print OUT "got a connection from: $client_host", "[$client_ipn
+um]\n";
close(OUT);
# send them a message, close connection
#print CLIENT "Smile from the server";
close CLIENT;
}