> What were the security problems?

> They don't even allude to the existence or detection of any specific security problems

Arguably the product itself. Which is another reason they might be vague about it. Because to talk about those security problems would taint the entire product and they can't do that if they aren't willing to completely scrap it.

People have been talking about how the data in here is similar to what may be already existing but that's far from the truth. Yes, these companies have a lot of data on us, but this is a significant step forwards in the granularity of that data. It's also worth noting that hackers could not get into your computer and assume that your computer not only has a keylogger that they can access to further compromise your system (and other systems/accounts) but that they can also obtain screenshots. These increase user risk significantly and greatly reduce the requisite technical skill needed for those infiltrating machines.

Similarly, many have pointed out the potential connections to Chat Control[0] and how such systems can likely be used by many companies to be exploitative of workers. While you may trust your company/partner/significant others/government and so on, it is important to remember that not everyone has such luxuries. It is also important to remember that such things can change. Even in the US there are high risks of potential abuse: such as police obtaining a warrant to get this data to see if someone is trying to obtain abortion medication. Regardless on where you fall on that specific issue, you can replace it with any other concerning issue and I'm sure you wouldn't like that (guns, religion, gender identity, political affiliations, and so on). So even if you trust Microsoft to not give away this type of information nor to provide authorities access (which often includes authorities not in your home country), then you must ask if the benefits are worth the costs. And not just for you, but for others.[1]

> It sounds to me like they're figuring out a new marketing approach

I suspect this is correct and as segasaturn suggested, turned up the heat too fast. I also suspect that this type of data invasion can be much more easily understood by the general public, who often struggle with understanding what metadata is and how it is/can be used. It does require technical knowledge for this and is often non-obvious, even for people who are well above average in technical literacy (as is the average HN user).

[0] Specifically we should note here that Chat Control would force Microsoft to use this system in a much more invasive way. We lambasted Apple over their proposal for CSAM detection, including the potential risks of abuse even if it were theoretically impossible to avoid hash collisions. Having Relay would require Microsoft to implement such a system and that's why there are many conspiracies arising that Relay is specifically intended for Chat Control, because true or not it would likely have similar outcomes. We'll see if Apple revisits the idea, and the recent WWDC doesn't rule out such a possibility https://www.patrick-breyer.de/en/posts/chat-control/

[1] https://www.youtube.com/watch?v=goQ4ii-zBMw