From Basic Set p76, we have the Digital limitation to Possession:
Digital: This limitation is only available to Digital Minds (p. 48). You take
over computers, not living bodies. The
target system must be connected to
your current host computer via a network, and you must have complete
access to it – voluntary or otherwise
(see Computer Hacking, p. 184). The target computer’s hardware must be complex enough to run your computer program; in general, its Complexity must
be at least half your IQ (round up). You
can also take over a computer using a
copy of yourself while leaving the original intact! However, unless you have the
Digital version of Duplication (p. 50),
any system you take over this way
becomes an independent NPC that
thinks it is you. This can be good or bad
– the duplicate could become any type
of Associated NPC (see p. 31). -40%.
A quick check of the campaigns book shows that 2004-era desktop systems are Complexity 4 (Basic Set p472), although super computers and the like would obviously be more complex.
Now, I understand the reasoning that a desktop PC couldn't handle running an advanced AI- but that's completely ignoring how fantastical digital possession would be in the first place. Such technology capable of completely overriding another system and taking it over would surely be capable of dealing with the Complexity issue.
The other big design fail here is that Possession seems strictly inferior to Mind Control with the Cybernetic Enhancement/Limitation:
Cybernetic: You can affect entitiesSo let's compare. Digital Possession with Full Memory Access, and Telecontrol 1 is going to run you 120 points. You're only able to possess machines with complexity equal to half of your own IQ- so in a TL8 setting your IQ is maxed at 8 if you want to possess a rudimentary desktop PC. Otherwise you're stuck possessing far more complex machines, all of which are going to be incredibly rare. You have to win an IQ vs. Will contest to succeed, even against non-sentient computers.
with the Digital Mind trait (p. 48),
including all ordinary computers.
Your IQ roll has a penalty equal to the
system’s Complexity. A nonsentient
system does not resist; just roll vs. IQ -
Complexity to succeed. +50%.
Mind Control with Cybernetic Only will run you 25 points. An IQ 16 AI with it will take over a desktop computer ~74% of the time with an unopposed IQ-Complexity check, and then be able to tell it to dump data logs, open the security gate, and delete the logs that the intrusion by the AI ever happened.
Even if you need a version of Telecontrol (wifi) to make Mind Control work with machines at a distance, there's no way in hell that's going to overcome the 95 point gap between the advantages.
While I'm ranting about GURPS:
Telecommunication (Internet/Wifi) never made it into the Basic Set or Powers? Really?