Oracle can target cameras on unrevealed tiles, and cameras protected by Null Drones, which other programs cannot target. Oracle cannot target inactive cameras, or cameras which are rebooting. If there are no cameras for Oracle to target, then the program cannot be used; instead, the message “no remaining uncaptured cameras” is shown.
If you can afford the PWR for it, then Oracle is very useful for exploration, since it can hack cameras you have not yet discovered. Even though it targets cameras randomly, the cameras' vision can show you the locations of guards, Corporate Safes and sometimes the exit room. Oracle also tells you when it cannot target any more cameras, which is valuable information — when this happens, there is no need to peek for cameras before entering a room, though you may still need to peek for other dangers.
Oracle hacks cameras however many firewalls they have, so its PWR cost per firewall hacked depends on the number of firewalls. It is more efficient at higher mission difficulties, but still a valuable program at lower mission difficulties for its exploration benefits. It is best to explore early, so you will want to pair Oracle with a generator which gives a lot of PWR early. Seed is a good choice, as it lets you use Oracle for 0 PWR every turn, meaning you can hack all cameras in the facility before alarm level 2.
Oracle is generally safe to use because daemons are not initially installed on cameras, except by Fractal 2.0 in Endless mode. However, if Fractal or something else installs a daemon on a camera during the mission, then Oracle has a risk of triggering it.
While Oracle technically meets the definition of a breaker program, it is not functionally a breaker since you can't use it to hack anything other than cameras, and unlike all other breakers you cannot choose which camera to hack with it. Oracle is at its worst when you need to hack a specific camera, especially if you do not intend to explore the whole facility. The probability of hitting the one camera you want to hit is typically quite low, so it may take several uses, costing a lot of PWR. In that case you should normally use a different breaker rather than gambling, though sometimes you have no option.