A coworker and I put a couple pieces of open source software (OSSEC and Snort) together to respond to certain types of automated attacks we were seeing in our IDS (we use Snort in this case). Prior to this, an engineer would manually respond to alerts by logging into our firewall and blocking the IP address causing the alert. This process was tedious, repetitive, and time consuming. By the time the firewall change would be pushed, generally the scan (it was usually a scan) was over and the attacker had moved on. So we took advantage of a feature in OSSEC called “active response”, which is used to react to events on the network. OSSEC was configured to watch for Snort alerts, and would run a script on our Internet routers (running Vyatta core 6.3) to block the IP for 10 minutes. This response runs almost immediately. We hand selected alerts that we had associated with simple scans, such as FTP Brute Force attacks, and set them up to block the addresses. But this wasn’t enough for us.