The biggest risk of "sharing DNA" is pregnancy.

...I'll show myself out.

I can easily imagine a reality where insurance companies have access (intentionally or accidentally) and give you a higher premium because they found something that makes you more predisposed to some ailment.

The above is pure speculation, but it's only one security breach or bag of money away. It's never safe to assume that a your data is 100% secure at a (presumably) benign company. As curious as I am regarding certain aspects of my heritage, the fact that I have no control over what they do with the info is keeping me on the bench.

23andme already got hacked and 7 million people's private data was compromised:

https://www.theguardian.com/technology/2023/dec/05/23andme-hack-data-breach

You can call me paranoid, but the first thing I thought of when I heard about it was how excited the Nazis would have been to access a database like that when they came into power. Imagine knowing the names and addresses of whatever Undesirables you wanted to single out, and exactly what percentage of "impure" they were. Ethnic makeup information can also be used against you in things like gerrymandering congressional districts to hand select voters and disenfranchise minorities. It's pretty safe to assume that once your genetic profile has been gathered by a private company, it's vulnerable to all sorts of bad actors gaining access and using that information. Would you want the KKK or the Proud Boys knowing just what percentage black you are? No thanks.

The big real-world implication I'm aware of is that law enforcement can match DNA they found somewhere against 23andme's database. Then if you (or any of your relatives!) are in the database because they've ever used 23andme, they'll find that out, and they can use it to investigate or prosecute you.

Whether you think that's a good or a bad thing depends a lot on whether you think the cops should be able to succeed if they get a hold of someone's DNA and are looking for the person to match their sample against... that success is, to me, much more likely to be a good thing than a problem, but that may not be the consensus view here and it's certainly a massive, massive privacy implication.

Your clone escapes, hunts you down, kills you, fucks your wife, and replaces you

At least in some circumstances, the risks of sharing your DNA include having children...

If you’re like me, you could find out at age 38 who your true biological father is, and contact him for the first time. It may spiral you into an identity crisis, wondering if you should change your name and the name of your children. Here’s the thing though, my biological dad didn’t share his DNA. His first cousin did, and I contacted him.

As others have said, because you share your DNA with all of your relatives, it’s already not 100% private. One or more of your relatives has already tested their DNA. The most genetic privacy you can get would be for nobody to know who you’re related to. How tightly do you protect that information? Changing your name would be a good first step.

Insurers get hold of it and disqualify you for health, life and disability insurance based on genetic markers.

Someone could build an army of clones of you, launch galactic war, and then you'd be hated all over the galaxy. Assuming you have good genes. Probably they made a bad movie about this.

we already know 99.9% of your DNA, it's over

If anyone in your family starting at like your second cousin and closer have already done DNA testing then the cats outta the bag on worrying about your privacy.

In the US, insurance companies cannot discriminate based on your genetic data, contrary to what many people in the comments are saying.

https://www.hhs.gov/hipaa/for-professionals/special-topics/genetic-information/index.html

These services, like most companies will store your data indefinitly, and can be hacked. You cound end up with your name, what ever infromation the service gave you, and contact info on the internet. This is not the end of the world, but something to be aware of.

All who could have an idea of what to do with it could seek a way to get that data out of every company or gov that have it for their specific reasons, no matter if data was collected lawful or not, or if access to the data is then lawful or not.

1. search for source of evidences on crime scenes: if one of your relatives happened to have been (related to crime or just bad luck) at a place where later on some evidence was collected, you might cause trouble for them bcs your data is very similar to theirs and that is obvious to laboratories. depending on the the "later on" current state of technology it could affect relatives more than two or three steps away from you. if you live in a country where law enforcement gives a shit about truth and just seeks for one argument to punish just anyone they can point a finger at, that could become a huge problem for the whole family then just because there was data that could have been abused.
2. illegal organ traders could - once they have access to your data - think you or your relatives could be a source of nice income if a client of theirs happen to pay enough. however you will probably never know as the illegal organ traders are unlikely to ring the doorbell to ask nicely for a contract. How much do you think would a richie in personal needs pay for "spare parts" if those who deliver them wants him to just never ask where it came from ? does it matter if such organ teaders could know a "compatible match" by data only? maybe not because they might know tomorrow or someone might put up an AI to do the matching (does it matter if that matching by AI is correct then? i guess such traders don't really care and their customers probably, but wouldn't that be possibly too late then?)

For me the latter is actually enough to not willingly give my DNA data to anyone. for no reason. gov might already have it (covid probes had been collected and frozen at least) but actively pushing your data out inzo the world would be insane IMHO.

Laboratories often use Microsoft Windows, Microsoft Active Directory and Microsoft Exchange, thus i personally see no reason to NOT believe that any data they have received once in time would - sooner or later - end up rotating uncontrolled in the hands of uncountable criminals waiting for any chance to make quick or huge money out of it.

I would never allow my DNA to be characterized or sequenced outside of a medical setting where strict privacy laws are in place.

It doesn’t matter if you use a service or not. Someone in your family most likely has DNA on file, either through voluntary submission, like 23andme, or through law enforcement, military government interactions that require submission. Once a family member is on file, it’s easy to ID you. Many crimes have been solved this way. Point being, doesn’t even matter if you try to keep private, if a nation state or three letter agency wants you, you done. If you’re worried about some company having your data just don’t participate in any of them… pretty much all you can do currently.

https://www.dnasquirrel.com/ provides some guidance on how to get DNA results while maintaining privacy. I haven’t tried it yet, but I’d like to hear if anyone has.

I was wondering about this for a while, is there an option to have a dna test like anonymously?

Forensic data on you is already pretty easy to obtain unless you're taking special effort to avoid it being taken. Also when you get arrested they take whatever biometrics they like. The info on you those DNA testing companies are getting is info already easily available to the government. I guess if you're concerned about your DNA being used to tailor ads to you, not just to criminalise you, it could be an issue, but idk I don't think your DNA can really predict what ads will be effective on you.

Babies, I guess

Those two apparently don't allow law enforcement access to their databses (yet?) even though I seem to remember they do. But others do:

https://www.nytimes.com/2021/05/31/science/dna-police-laws.html