How Sudoku Challenge handles your data — built on blockchain with privacy by design. Effective 14 February 2026, last updated April 2026.
Sudoku Challenge (sudokuchallenge.com) is built on the Internet Computer Protocol (ICP), a decentralized blockchain network. Unlike traditional web applications, your game data is stored in on-chain smart contracts — not in a private corporate database. This architecture gives you stronger privacy guarantees than conventional websites.
The following data is stored on the Internet Computer blockchain in our smart contract (canister), as needed to provide the game's functionality:
We collect the absolute minimum data needed to run the platform. We do not collect email addresses, real names, phone numbers, physical addresses, IP addresses, location or GPS data, browser fingerprints, browsing history, or payment card information.
Some data is stored locally in your browser (via localStorage and sessionStorage) to improve your experience and never leaves your device: game settings (theme, difficulty, board options), current puzzle progress so you can resume, a randomly generated guest username for non-authenticated play, and tournament notification preferences. You can clear this at any time through your browser settings without affecting your on-chain profile, rating, or game history.
Sudoku Challenge runs on the Internet Computer Protocol, a public blockchain that hosts both the frontend and backend of the application. There is no central corporate server: data lives in a smart contract on a decentralized network of independent nodes. Internet Identity provides passwordless, anonymous authentication, the smart-contract code can be verified by anyone, and your browser communicates directly with the blockchain with no data-collecting middleman. As administrators we retain the ability to enforce community guidelines — suspending or banning accounts that violate policy, removing inappropriate content, and adjusting ratings in cases of confirmed manipulation.
Google Analytics is used to understand how visitors interact with the site (pages visited, session duration, general geographic region) via cookies that collect anonymized usage data. We also use third-party advertising partners that may use cookies to serve and measure ads. You may opt out of Google Analytics with the official Opt-out Browser Add-on, and opt out of personalized advertising through your browser settings or ad-blocking extensions. We do not sell any data to third parties.
Sudoku Challenge offers a Premium subscription that removes all ads. When ads are removed, third-party advertising scripts do not load, so no ad-related cookies or tracking are active on your session. Google Analytics is still used for general site improvement, which you can opt out of separately.
You may clear your local browser data at any time without affecting your on-chain account, stop using the service at any time, leave tournaments before they start, request information about data stored on-chain under your principal ID, opt out of personalized advertising, and contact us with any questions or concerns.
Sudoku Challenge does not knowingly collect personal information from children under 13. Because we don't collect personal information from any user (no email, name, or location), the platform is safe for users of all ages. We encourage parents and guardians to supervise children's online activity.
If you are in the EEA, UK, or Switzerland, the GDPR gives you rights over your personal data, including access, erasure, portability, and objection. We process data based on legitimate interest (analytics, security) and consent (advertising cookies), which you may withdraw at any time. Game data is stored on-chain under a cryptographic principal, so it is already pseudonymous. To exercise these rights, email support@sudokuchallenge.com.
California residents have the right to know what personal information we collect, request deletion, and opt out of sale. We collect minimal data (no email, name, or address) and we do not sell personal information — we never have and never will. We will not discriminate against you for exercising your rights. To make a request, email support@sudokuchallenge.com.
When you subscribe to Premium, payment is processed by Stripe, Inc., a PCI-DSS Level 1 certified processor. We do not store, process, or have access to your full card number, CVV, or bank details. We store only your subscription status and Stripe customer ID, linked to your Internet Identity principal. See Stripe's Privacy Policy.
User-uploaded avatars are deleted after 6 months of inactivity (reverting to the default avatar); inactive accounts may be permanently deleted after 24 months. Any login resets the inactivity timer, and active Premium subscribers are exempt from both avatar and account deletion. Subscription data is retained for the duration of your subscription plus 90 days after cancellation. You may request deletion at any time via support@sudokuchallenge.com.
We don't collect personal information. Your game data lives on a decentralized blockchain. Third-party services (Google Analytics and advertising partners) may use cookies, which you can opt out of. Payment processing is handled securely by Stripe. We never sell your data.