1. Detecting the Wireless Network [SR4 p225]: In order to hack a system you first must locate the wireless network that you want access to. Doing this is an easy task and requires no test and is considered a free action.
If you are in an area of high wireless activity the GM may require you to make a Electronic Warfare + Scan (GM determined threshold, 1 combat turn) extended test in order to filter through all the traffic for what you want.
It may be that the target network is in hidden mode. In order to identify a hidden network a Electronic Warfare + Scan (4) test is required.
If you are more generally trying to locate any hidden nodes in an area then an Electronic Warfare + Scan (15+, 1 combat turn) extended test is required.
2. Breaking In [SR4 p221]: A Hacker will take to approaches to breaking into a system. Ideally she would probe the target over time to identify any weaknesses in its security. However she may not always have time for this and will have to hack on the fly.
a) Probing the Target: This is the process of tentatively poking and prodding at the system in order to find vulnerabilities that will make it easier to gain access. The hacker must make a Hacking + Exploit (target's System + Firewall, 1 hour or 1 day) Extended Test. This will give the hacker personal account privileges, increase the threshold by +3 for Security privileges or +6 for Admin privileges.
Once the threshold has been achieved and the account created the hacker only has to use a complex action in order to break into the system. No further test is required.
At this point the system gets a chance to try and detect the hacker by making a single Analyze + Firewall (hackers Stealth) test. If it succeeds then an alert is triggered.
b) Hacking on the Fly: If you think of probing the target as using a lock pick then hacking on the fly is the same as using a crowbar. It can be used to open a door at the end of the corridor your being chased down and then lock it behind you or to access the cameras ready to catch you sneaking into a warehouse. It's much quicker but leaves you more vulnerable to detection.
A Hacking + Exploit (targets firewall, 1 initiative pass) Extended Test is required to access the target system with Personal account privileges, as before increase the threshold by +3 or +6 for Security or Admin privileges respectively.
Remember I said that it was much easier to be detected while hacking on the fly, well every time the hacker makes a test the system gets to make an Analyze + Firewall (Hacker's Stealth) extended test. If it succeeds an alert is triggered.
Once a hacker is into the system she is free to go about performing any tasks that her account privileges permit. However she should still be on alert for roving security hackers and Intrusion Countermeasures (IC). In addition if an alert has been raised the system is likely to take active measures to deal with the hacker.
3. Log Off [SR4 p220]: No test is required to log off; it is merely a Simple Action. The exception is when a hacker is engaged with Black IC [SR4 p231].