The Tech Skills in System Shock 2 are more or less your utility belt - they govern most of your non-combat abilities, though many of them have an indirect correlation in that they provide some sort of passive benefit or allow you to improve your weapon capabilities. Each Tech Skill reduces the difficulty of a given task by 10%, though they do not reduce the number of ICE Nodes. Tech Skills are also governed by software, which must be found in the environment or purchased from Replicators, with a maximum level of 3 for each category of software. Last, most technical tasks have minimum requirements, so boosting your Tech Skills is necessary to even attempt them.

Below, you'll find a more detailed list of the different Tech Skills, including evaluations of each of them.

Hack

Governs: Success in hacking keypads and secure crates Maximum value: 6 Evaluation: Hack is the explorer's skill - it allows you to get into nplaces you normally wouldn't be able to without a passcode, it lets you get extra loot from locked crates, and it even helps you during the final boss battle. Hack is probably the most useful Tech skill next to Maintenance, simply due to the frequency at which you'll find it comes in handy, and you'll gain access to a lot of extra items with it, as well as a few weapons you normally won't be able to obtain until later on. While the loot in those locked crates varies from being extremely useful (the only non-broken Fusion Cannon) to no better than average, it all boils down to more equipment and items, and that's never a bad thing. The fact is that Hack pays off the biggest dividends of all Tech skills, and on a pure utility basis, that makes it worth at least putting a few points into. While bringing it all the way up to maximum probably isn't a bad thing, however, it does eventually suffer diminishing returns (albeit not as badly as the other Tech skills), and there are enough ICE-Picks available to render a full investment unnecessary.

Repair

Governs: Success in repairing weapons and Replicators Maximum value: 6 Evaluation: Despite what it sounds like, Repair is generally not very useful next to the other Tech Skills. While there are a few Replicators that require Repair to make operational (including one that sells the Recycler earlier than normal), the benefits of this are questionable in the grand scehme of things, as there's rarely a time when you won't have convenient access to a Replicator, and no sure bet a broken one will be useful to you. Repair also allows you to restore broken weapons to working order, and many weapons, such as the Grenade Launcher, Statsis Field Generator and Fusion Cannon, can be found earlier in broken form. While not having to use Maintenance on your weapons can be a boon, Maintenance also provides too many other passive benefits to ignore. Last, Auto-Repair Units are common enough that most players will have enough in the odd situation a weapon does break down. Simply put, unless you really want that Fusion Cannon early, or want to bring every Replicator online, Repair can be ignored.

Modify

Governs: Success in modifying weapons Maximum value: 6 Evaluation: Modify is a bit of an odd skill in that it's typically only going to be used a few times throughout the game. Weapons only need to be modified a maximum of two times, and chances are you'll only be using a few primary ones throughout the game. Furthermore, French-Epstein Devices can be used to automatically modify any weapon, and there are enough in the game that, for an exploration-minded player, there's little reason to put a single point in Modify. However, in a multiplayer game, the number of French-Epstein Devices per player decreases, so Modify becomes more useful as a secondary skill on one, in order to do the modifying for everyone else.

Maintenance

Governs: Success in maintaining weapons, maximum equipment charge Maximum value: 6 Evaluation: Keeping your weapons in working order is a necessary evil in System Shock 2, and the drain on your Nanites spend in maintaining them will be lessened with each level in Maintenance, not to mention that it improves the efficiency of your Disposable Maintenance Tools (though Maintenance has no effect on actually repairing broken weapons). The secondary benefit of Maintenance, however, is arguably even more useful. With each level, you can hold an additional 10% energy charge in your equipment. If you rely on Implants, Energy Weapons or Powered Armor, Maintenance is absolutely indispensible, as it reduces the number of Portable Batteries, Electron Cascades, and trips to Recharging Stations you need. While maxing this one out isn't necessary, getting 3 or 4 points in it is almost essential.

Research

Governs: Success in maintaining weapons, maximum equipment charge Maximum value: 6 Evaluation: Research is the third-best Tech skill, behind Hack and Maintenance, due to the fact that researching the various organs found on dead enemies will in most cases yield substantial damage bonuses against them (+25%). Additionally, certain items like the Psi Booster and Annelid Healing and Psi Glands are only available after being researched, the latter two of which are essential on Impossible difficulty. You'll be forced to grab at least one level in Research on Hydroponics, in order to research the Toxin-A Sample, but it's best to get that level back on MedSci, as the damage bonuses toward Hybrids and Monkeys will pay off, and you'll get the Cyber Modules back on Hydroponics anyway. However, past about level 3 (you can get away with level 2 if you have a LabAssistant(TM) Implant), Research becomes significantly more specialised, as it's only necessary for some of the Annelid Implants, and the Exotic Weapon branch. If you want to use those, put a couple more points into Research, but otherwise you can safely leave your Research at 2 or 3.