I tried looking up some of the details on the recent Australia deal, but it's hard to find anything from what would appear to be a neutral source. What does look like what happened - weather stations in some areas measured temps that were lower than -10C (14F). For whatever reason, the "system" had some sort of filter that was set to a low limit of -10C. Temps that were measured below -10C were recorded as -10C until somehow recording stopped, probably because the temps were out of limits for some amount of time. Not necessarily "cooking" the numbers, but the Australia wx service says they have corrected or removed the s/w filters that caused that problem. My guess: They had some filters in place that someone simply put in as "if temp < -10 then temp = -10" to try to account for a failed temperature sensor. There was probably a better way to do it, or they could have chosen a much different number.
Temperature "adjustments" seem to be common. Temps for every point on earth can't be taken, so fairly large regions need to be averaged and interpolated. But what happens when a recording station that was out in a rural field is now surrounded by a mall? That affects the temps at that station, so how do you adjust out the local terrain influence? If you move that station somewhere else, you've just affected the data that station is recording - how does that affect the average of the area and how to weight the results? It's not trivial, and there is a lot of money at stake which makes it political, too.