Privacy Policy

1. Who we are

This policy governs the collection and processing of personal data by the Thuộc Từ app ("We", "Us"), operated by Shijiazhuang Jizhan Technology Co., Ltd. ("the Company"). Contact us at support@91word.com for anything related to personal data.

2. Data we collect

Category	Details	Purpose
Account data	Phone number (+84) for registration/login; device identifier (Android ID) used to create the guest trial account	Account creation and protection, identity verification on recovery
Learning data	Selected word books, per-word progress, review schedule, study time and results, study-streak statistics	Core functionality: study planning and the spaced-repetition (Ebbinghaus) algorithm
Transaction data	Order references and VIP/coin subscription status purchased via Google Play Billing	Granting VIP benefits, verifying purchases. We do not collect card numbers — payment is handled by Google
Content you provide to AI features	Words/text you select for generated readings and stories; audio recorded for pronunciation practice	Sent to the language-processing service (see sections 5 & 6) and results returned to the app
Technical data	Device model, Android version, crash logs	Debugging and compatibility optimisation

We minimise collection: no access to contacts, messages or location.

3. Legal bases and purposes

• Performance of the service contract: purposes in section 2;
• Your consent: at first acceptance of this policy and when enabling features with additional collection;
• Legitimate interests: abuse prevention, payment-fraud prevention, system security;
• Legal obligations under Vietnamese law.

4. Storage location and retention

• Personal data is stored on secure servers operated by the Company located in Asia, with transport encryption (HTTPS/TLS).
• Retention: account and learning data for the lifetime of the account; technical logs up to 12 months.
• After account deletion, your data is erased within 30 days, including periodic backups.

5. Sharing with third parties

We never sell personal data. Data is shared only with:

• Google Play Billing — payment processing (see Google's privacy policy);
• Google Firebase (Analytics, Crashlytics) — anonymised usage statistics and crash reporting;
• Firebase Cloud Messaging (Google) — collects a device push-notification token after you consent to this policy, solely to send study reminders. You can turn reminders off in Settings; the push token is removed from our systems when you delete your account;
• AI language-processing provider — receives text/audio content stripped of identifying fields (no phone number, no user code) to generate lessons and score pronunciation;
• SMS provider — delivering one-time verification codes;
• Competent authorities when required by law.

6. Cross-border data transfer

To operate AI features, your input content (anonymised as described in section 5) may be transferred to processing systems outside Vietnam. Such transfer complies with Vietnam Decree 13/2023/ND-CP on personal data protection; we apply protective measures (data minimisation, transport encryption) and disclose it here for your consent when using AI features.

7. Your rights

Under Decree 13/2023/ND-CP and this policy you have the right to:

• Be informed, access and correct your personal data;
• Delete your data (account deletion — see account deletion page);
• Withdraw consent and request suspension of processing;
• File complaints and denunciations about data processing.

Send requests to support@91word.com; we respond within 30 days.

8. Children

The app is intended for users aged 13+. We do not knowingly collect data from children under 13; such data will be deleted upon discovery.

9. Security

We use TLS for all traffic, isolated data systems, least-privilege internal access and periodic backups. No method is absolutely secure; please never share your OTP code with anyone.

10. Changes

Material changes will be posted on this page with an updated date and announced in the app.

11. Contact

Operator: Shijiazhuang Jizhan Technology Co., Ltd.
Email: support@91word.com