Asymmetrical multiplayer will allow you to invade one another's games.
By Tim Colwill on June 14, 2013 at 11:59 am
The multiplayer in Ubisoft’s upcoming Watch Dogs will consist of asymmetrical warfare where players attempt to hack into each other’s games, reports Ubisoft in a blog post explaining the mechanics.
Other human players can jump into your world, appearing to you as regular NPCs. You’ll be then able to attack their phones after tagging them, and attempt to hack into and upload a virus to them. The attacked player — who could be you! — will then be notified that an attack is happening, and have a set amount of time to find you and stop you (often violently).
You can, naturally, jump into other player’s worlds and try to do the same to them. If you enter another player’s world you can also grief them, ramming them with cars and doing other fun things. However, this only works out in the open world — once you’re in a mission or a sidequest, you can no longer be interacted with by guest players in your world.
This multiplayer component can be completely disabled if you like, so you’re never forced to share your world with others. However, quite frankly, it sounds like a hilariously good time.