Once inside a person, nanobots start replacing natural organelles and tissue. That's how you live longer: the little bots are better at repairing themselves and working properly for decades.
Eventually they will replace all the enzymes and proteins involving synapses and proper neuron functioning. The user is thus immune to diseases ranging from Alzheimer to rabies.
The downside of this is that you are now bound by an EULA. The moment you skip a monthly payment of your nanobot licensing, they shut down. That is death in a millisecond. You won't feel a thing - because feeling itself is a function of the bots now. That is the most swift death short of being vaporized by a nuke or a supernova.
For the outside world, you are braindead. Your organs will last a few more minutes - more if urgent care can be provided on short notice, allowing for them to be harvested.
If Metasoft - an Applebet Company TM wishes to be particularly cruel, they can project a mental image saying "We are sorry, but you don't have enough money to live" for the user a moment before deactivating their account.
Within this context, a hacker could trigger account removal by emptying someone's bank account; They could also cut someone off the network so the nanobots are not notified of the latest payments. Or, you know, the user simply lost their job and outlived their usefulness to the eyes of a society that values capital over human life.