A young brother and sister within a virtual reality environment encounter people who are violating the rules. It’s well done, with a couple of good revelations toward the end. The story stops short of exploring the ideas that it raises. It merely opens the door and leaves the rest for the reader to imagine.
"Cheats" by Gwyneth Jones, writing as Ann Halam, first published in the anthology Starry Rift (Viking, 2008) edited by Jonathan Strahan
Link: Year’s Best SF 14summation and table of contents