Case 16: Murder Sudoku
Privacy policy
Last updated 1 October 2026
There is no account
Case 16 has no sign-up, no login and no password, and never asks for your name or email. The first time it runs, the app generates a random identifier on your device. It is not linked to your name, your email address or your Apple ID.
What that identifier is for
Two things. When you close a case, the app sends us which case it was, how long it took and how many hints you used, together with the identifier — so your record can be kept for you. It goes with every step of the monthly case too (below). And it is the customer number our billing provider uses to know whether you have paid to remove ads. Downloading the ordinary cases sends no identifier at all.
It survives reinstalling
The identifier is kept in the iOS keychain rather than in ordinary app storage, so deleting Case 16 and installing it again gives you back the same one — and with it your subscription. That is deliberate: with no account, anything that forgot the identifier would forget what you paid for. It is removed when you erase or reset your device, or if you ask us to delete it (below).
What stays on your phone
Your progress through a case, your saved boards, your solved-case record and your settings are stored on your device. A case you have solved offline waits there until it can be sent.
Advertising
Every case is free, and ads pay for them. They are served by Google AdMob. In the European Economic Area, the UK and Switzerland, Google’s consent form asks first whether ads may be personalised; wherever you are, Apple’s prompt asks whether Case 16 may use your device’s advertising identifier, and nothing uses it unless you allow it. Google may still collect information such as your device type, an approximate location from your network address, and how you interact with an ad, to show it and to measure it. That is Google’s processing, described in Google’s own policy. In the European Economic Area and the UK you can change your ads choice at any time with the Ad privacy choices row in the app’s Detective tab; anywhere, you can change whether Case 16 may use the advertising identifier in iOS Settings, under Privacy & Security, Tracking. If you subscribe to remove ads, the ad software is not started at all and you are not asked.
The monthly ranking
Once a month there is one ranked case, and you file one time for it. Starting it starts our server’s clock, which runs in real time until you solve it; filing the time uses your attempt. We record the identifier, when you started and how long you took, until about a week after the month ends, then delete it. The ranking shows other players only a name generated from your identifier, such as “Quiet Falcon 42”, and your time. It never shows the identifier itself.
Purchases
Removing ads — by the month or once for good — is handled by Apple and by RevenueCat, our billing provider. We never see your payment details. RevenueCat tells the app whether ads are off for you, keyed to the identifier above.
What we do not do
We use no analytics or crash-reporting software, we do not sell anything about you, and we do not track you across other apps or websites ourselves. Apart from ads, as described above, nothing about how you play leaves your phone except a closed case and the monthly case.
Where this happens, and for how long
Our server runs on Cloudflare’s network, which is worldwide, so a request may be handled outside the country you are in, including in the United States. Cloudflare keeps short-lived logs of the requests it handles for us — the time, the address it came from and what was asked for — which we use to keep the service working, and which expire within days. Your solved-case record is kept for as long as you play, so it is there when you come back. Everything travels over an encrypted connection. Cloudflare, RevenueCat and Google are bound by contract to protect what they handle for us at least as well as this policy does.
Playtesting
An unlisted page on this site lets invited testers play unpublished cases and leave notes. It keeps a random tester identifier and the tester’s access code in the browser, and sends the notes to us with that identifier. It is not part of the app.
Your rights
Because there is no account, what we hold is a list of closed cases attached to a random identifier. You can ask us for a copy of it, ask us to correct it or ask us to delete it, and you can complain to the Spanish data protection authority (the AEPD) or to your own. We keep your record to provide the game you are playing, and your subscription status to provide the subscription you bought; ads are shown on the basis of the choice you make in the consent form and the tracking prompt.
Children
Case 16 is not directed at children under 14, the age at which Spanish law lets a person consent to this kind of processing themselves, and we do not knowingly hold anything about anyone younger. If we learn that we do, we will delete it.
Deleting your data
Deleting the app removes everything stored on your phone except the identifier, so a reinstall does not cost you your subscription; erasing the device removes that too. To delete everything we hold for your identifier — your closed cases, times and monthly ranking entry — use Delete my data in the app’s Detective tab; it erases them from our server and from your phone at once. Two things outlast it for a short while: the ranking’s top page is kept for up to a minute, so your generated name and time may still show there for that long, and Cloudflare’s request logs (above) expire on their own within days. If you had started this month’s ranked case, we keep a mark that this identifier used its attempt — with no time and no start in it — so that deleting your data does not hand you a second one; it is deleted with the rest of the month’s ranking. You can also have us delete the identifier and every closed case attached to it by writing to apps@blankhexadecimal.com. The Help & contact row in the app’s Detective tab opens an email to that address with your identifier already in it, which is the one thing we need to find it. Deleting it does not cancel a subscription — that is done in your Apple ID settings.
Changes to this policy
If what the app does changes, this page changes with it, and the date at the top says when. We will not quietly start collecting something this page says we do not.
Who to write to
Case 16 is operated by BLANK HEXADECIMAL, S.L., Calle Illescas 46, piso 11, puerta 1, 28024 Madrid, Spain, which is the data controller for the purposes of data protection law in Spain. Write to apps@blankhexadecimal.com.