Evidence of Reviewing Scams in Major AI/ML Conferences? I have recently heard a few independent rumors about massive collusion amongst reviewers in major AI/ML conferences. The way this works is that a large group of program committee (PC) members start a chat group (on WhatsApp/Telegram etc.) and share their assigned papers; other members of the group flag papers that are theirs and get the "insiders" to score them higher. 

To make things concrete, Alice and Bob start a chat where both share their assigned papers. Alice sees that Bob's batch contains one of her papers, and asks Bob to write a glowing review of that paper. 

Are these rumors substantiated? Has anyone else heard of this going on? If it is as widespread as I was led to believe, what does this mean for the review process in these conferences and what countermeasures can we take?
The top AI/ML conferences like NIPS have something like 2500 reviewers. There will probably be some bad apples in there who engage in the sort of behavior you describe. However, I would be shocked if this is happening at a large scale. The conference organizers would take action if they were aware of any such activities.

It sounds like you have no evidence of this. Frankly, it sounds like a typical conspiracy theory. Perhaps someone wishes to explain why their papers never get in but those from X, Y and Z always do, and decides that X, Y, and Z must be colluding. The true explanation will be a lot more mundane -- it's probably just that certain groups and people have more experience and have learned the "tricks of the trade" needed to publish papers.