In addition to the blatant example that Elm cites, I have seen numerous attempts to use the Great Hall as a place to coordinate efforts to help or hurt another House. During the run-up to the Inaugural House Cup, I witnessed some “Ravenclaws” and “Hufflepuffs” announce in the Great Hall that they were giving easy duels to Gryffindor to help in the battle against Slytherin. As a dueler, I have personally seen some “Ravenclaws” and “Gryffindors” whose accounts were obviously set up with the intent to help Slytherin. And I have heard from Gryffindor duelers that they have seen “Slytherins” obviously helping Gryffindor. All this in addition to the “Slytherin” accounts set up with intent to blow up cauldrons and lose the House points.
Because the cheating is so widespread, I personally think that it all evens out in the end – without giving any single House an advantage. However, I do believe it diminishes the experience. When the top Hufflepuff – HUFFLEPUFF!!! – is bragging in his own House Common Room (and on Twitter) that he is using scripts not only to duel all day but to toss 1000 gnomes out of the Weasley garden in a single De-Gnoming, something is broken in the Pottermore experience. But when the Slytherin Common Room becomes Ground Zero in the battle against cheating, then something kind of wonderful is happening.
Pottermore needs to tighten security, identify scripts, keep a closer watch on the Great Hall, and ban the cheaters. Ironic, I think, that it’s Slytherin leading the campaign. But let’s stand together in this, regardless of House.