Privacy Policy

Last updated: 9th June, 2023

This privacy policy describes the information that's collected when you use the website, how it's stored and how it's used. Your privacy is very important, so the site only uses the bare minimum of information for correct operation.

Before you use or submit any information through or in connection with the site, please carefully review this Privacy Policy. By using the site, you understand that your information may be collected, used and disclosed as outlined in this Privacy Policy. IF YOU DO NOT AGREE TO THIS PRIVACY POLICY, PLEASE DO NOT USE THE SERVICES.

Personal information

Information about your computer, including your IP address, operating system and browser type, is stored temporarily in log files and may be used for system administration purposes, such as diagnosing faults, analysing site statistics and maintaining security. This is common practice for almost every website in the world. The log files are kept for 3 days, after which they're deleted and the information is no longer accessible.

If you create an account, the site will collect and store:

  • A username chosen by you - this may be displayed to other users either now or in the future (for example, on leaderboards)
  • The e-mail address you provide - this won't ever be displayed to other users and is only used for account administration purposes, such as sending password reset e-mails

This information is stored in a password-protected database, using standard industry practices. It will not be shared with any third parties.

If the website sends you an e-mail - for example, the confirmation e-mail when opening your account - your e-mail address is stored temporarily in a log file for the purpose of diagnosing faults and maintaining security. The log files are kept for up to 2 weeks, after which they're deleted and the information is no longer available.

If you start an e-mail conversation by contacting one of the website's e-mail addresses, the e-mail conversation, including your e-mail address, will be archived in a mailbox and may be used to follow-up on your query (for example, to notify you that a feature you requested has been added), analyse trends (for example, to prioritise a feature that's been requested by multiple people) and maintain security.

You can ask for your conversation(s) to be deleted from the mailbox at any time by contacting the e-mail address below.


This website uses the hCaptcha anti-bot service (hereinafter "hCaptcha"). This service is provided by Intuition Machines, Inc., a Delaware US Corporation ("IMI"). hCaptcha is used to check whether the data entered when creating an account has been entered by a human or by an automated program.

To do this, hCaptcha analyzes the behavior of the website visitor based on various characteristics. This analysis starts automatically as soon as the website visitor visits the new user registration page. For the analysis, hCaptcha evaluates various information (e.g. IP address, how long the visitor has been on the page, or mouse movements made by the user). The data collected during the analysis will be forwarded to IMI when the website or mobile app visitor clicks the checkbox on the hCaptcha.

Data sent to IMI is scrambled/anonymized, and any data deemed to belong to a human is purged at the system's edge. Data deemed to be connected to an automated attack vector can be processed for up to 30 days.

Data processing is based on Art. 6(1)(f) of the GDPR (DSGVO): the website or mobile app operator has a legitimate interest in protecting its site from abusive automated crawling and spam. IMI acts as a "data processor" acting on behalf of its customers as defined under the GDPR, and a "service provider" for the purposes of the California Consumer Privacy Act (CCPA). For more information about hCaptcha and IMI's privacy policy and terms of use, please visit the following links: and

Other information

If you create an account, the site will additionally collect and store:

  • The puzzles you've solved
  • Statistics such as your solving times and the number of hints used

This information may be displayed on the website alongside your username, for example on leaderboards or summarised puzzle statistics. It may also be combined, anonymously, with statistics from other users to provide rolled-up totals or averages.

Cookies and Browser Local Storage

This website uses cookies, as almost every other website does, to give you the best possible experience. Cookies are small text files that are stored on your computer or mobile device when you browse websites. The cookies on this website help to:

  • Provide statistics for puzzles - number of attempts, average solving time, etc.
  • Personalise ad content

This website does not use cookies to:

  • Collect any personally-identifiable information
  • Collect any sensitive information
  • Pass personally-identifiable or sensitive information to any third parties

If your browser is configured to use cookies and you continue to use this website, it will be regarded as acceptance of this cookie policy. If you wish to remove or not use cookies from this site, instructions are included below, although if you do, the site may not work as you expect.

The cookies used by this site are explained below.

Session Cookie

This website uses a cookie that stores, on your computer, information about the puzzle you're currently solving. This cookie is used to gather statistics about the number of times each puzzle has been attempted and solved, as well as the average solving time.

If you create an account, this cookie also stores the page (within this website) that you will return to after you've signed in.

Browser Local Storage

In addition to the cookies above, this website stores the puzzle you're currently solving in your browser's local storage, if it's available, including any numbers you've entered, cage combinations you've faded out, etc. This enables you to continue from where you left off if you close your browser or switch off your computer and return to it later.

Google Analytics

This website uses Google Analytics to understand how users engage with the site. Details about which information is collected, how it's used and how to opt out can be found here. Google's policies prohibit personally identifiable information from being shared via Google Analytics


This website uses Cloudflare to enhance speed and security, meaning that all traffic passes through Cloudflare's servers before arriving at this website. To understand and control what information Cloudflare collects and stores, see their privacy policy here.

Disabling Cookies

You can usually disable cookies by changing your browser's settings. However, doing so is likely to limit the functionality of this site and many others, as cookies are a standard part of many websites' operation. If you do want to disable cookies, you can learn how here.

Access to your information

You can ask for a copy of your personal information by sending an e-mail to [email protected].

You can delete your account at any time by signing in, visiting the Account page and clicking Delete my account. This will immediately remove your personal information from the database, along with your saved puzzles, solving times, etc.

Compliance with the GDPR

The GDPR (General Data Protection Regulation) is important European Union legislation designed to protect the privacy of individuals and their data. The website operates in accordance with the principles of the GDPR. The data controller is:

Daily Killer Sudoku