System Level Filtering is another level of packet filtering in Outpost Firewall besides Application Level Filtering. It consists of:
System rules that let you create a rule that will be applied to all applications or rules that will allow or block low level system network activity.
Stealth mode settings lets you decide if your computer will respond to port scans or will silently block them, putting your computer in "stealth mode" to crackers.
ICMP filtering that lets you decide what types of ICMP message will be allowed or blocked.