Identity theft monitoring services always scare me. It seems like you are dumping a huge amount of information into a single system and just hoping the vendor is secure. I have access to one but refuse to put much information in. Is this mindset incorrect?
It reminds me of the recent Crowdstrike fiasco: apparently kernel level access was needed for their anti-malware to be able to properly work (because that way their net can cover the entire OS basically), but that high level of access meant that when CrowdStrike fucked up with an update, people's computers were useless. (Disclaimer, I am not a cybersecurity person and am not offering judgement either way on whether Crowdstrike's claim about kernel level access was bullshit or not)
In a similar way, in order for identity theft monitoring services to work, they surely will need to hold a heckton of data about you. This is fine if they can be trusted to hold that data securely, but otherwise... ¯\_ (ツ)_/¯
I share your unease, though I don't feel able to comment on the correctness of your mindset. Though I will say that on an individual level, keeping an eye on your credit reports in general (from the major credit agencies) will go a long way to helping there (rather than paying for serviced that give you a score and other fancy "features", you can request either free or v. low cost report which just has the important stuff you need to know.)
I also know that if you want to be extra cautious, you can manually freeze your credit so basically no new lines of credit can be opened in your name. This is most useful for people who have already been a victim of fraud, or they expect to be at risk (such as by shitty family, or a data breach). I don't know how one sets this up, but I know that if you did want to set up a new line of credit, you can call to unfreeze your credit, and then freeze it again when your application for the new credit is all done. I have a friend who has had this as their default for years now because of shitty family.
Yea that's a tough system to design for. Ideally you want sensitive stuff like that, where you don't care what the data is just that something matches it, stored as the results of a one-way hash function.
The problem is that most of the data you're going to want to secure is pathetically tiny. 10 digit SSN? My phone can brute force that in a few minutes if you're doing raw hashes. Gotta salt them. But now you have a tradeoff decision, salting every one uniquely is best but now your comparison needs to do [leaked data] × [customers] checks to find matches. Same salt on all of them and as soon as one is cracked they all are.