psad (Intrusion Detection and Log Analysis with iptables) psad is a collection of three lightweight system daemons (two main daemons and one helper daemon) that run on Linux machines and analyze iptables log messages to detect port scans and other suspicious traffic. A typical deployment is to run psad on the iptables firewall where it has the fastest access to log data. You can set email for alerts by setting ALERTSEMAIL: ALERTSEMAIL=alerts@example.com ./psad.SlackBuild You need at least these rules: iptables -A INPUT -j LOG iptables -A FORWARD -j LOG but more usefull will be something like this: iptables -A INPUT -i lo -j ACCEPT iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -p tcp --dport 80 -j ACCEPT iptables -A INPUT -j LOG iptables -A INPUT -j DROP please see documentation for more information. NOTE: psad requires several perl modules: perl-Bit-Vector perl-Date-Calc perl-IPTables-Parse perl-IPTables-ChainMgr perl-NetAddr-IP perl-Unix-Syslog these are included in sources, so you don't need to install them. But if you get some weird perl modules errors, you must uninstall previous psad version before bulding new one. Alternatively you can manually install this modules, all are available on SlacBuilds.