Hacking on the fly, I'm doing this wrong, aren't I? Options

[Jhaiisiin]

So with Hacking on the Fly, I've come to realize just how difficult it can be. If I understand the rules, once I'm detected as an intruder, the system stops accepting commands from me and/or boots my ass out of the system. If I'm a hacker running an average (Rating 4) Stealth program and hitting a system with a Firewall+Analyze pool of say 9 (not a crazy system), chances are I'm detected at the same time or before I finish hacking into the system.

The other night, we had our technomancer trying to break into an admittedly, very secure system and hacking on the fly only worked once out of like 10 times. She had her Stealth threaded up to 8 I think, but was only managing to toss a meager amount of dice at the rating 7 firewall.

Is this normal? Do you need more info from me? Am I misunderstanding the rules?