Human rights groups have condemned various war games for violating humanitarian laws and the Geneva Conventions.
The study, carried out by two Swiss human rights organisations; Trial and Pro Juventute, criticises games such as Modern Warfare 2 for allowing players to kill civilians, torture captives and destroy homes and buildings.
The twenty games scrutinised in the study also include Army of Two, Battlefield Bad Company, Far Cry 2, GRAW, Metal Gear Solid, Rainbow Six Vegas, Splinter Cell: Double Agent and Soldier of Fortune (we bet that last one scored well on the humanitarian stakes).
Human rights testers looked to see if the conflicts the games portrayed and what players can do were subject to the same limits as in the real world, reports the Beeb.
In particular, the testers looked for "how combatants who surrendered were treated, what happened to citizens caught up in war zones and whether damage to buildings was proportionate".
The results weren't good: "The practically complete absence of rules or sanctions is... astonishing," the study said.
Some games did punish the killing of civilians, it concludes, however many others allowed "protected objects" such as churches and mosques to be attacked.
The groups said games were sending an "erroneous" message that conflicts are waged without limits and that anything is acceptable in counter-terrorism operations.
"This is especially problematic in view of today's reality," the study said, adding that those who violate international law end up as war criminals, "not as winners".
The groups don't wish to make games less violent, they said, instead they "call upon game producers to consequently and creatively incorporate rules of international humanitarian law and human rights into their games."