These are the Terms Of Service (TOS) under which the aprs.fi service is provided.

1. The service is provided free of charge, as a public service, by a single individual, as his hobby on his spare time.
2. The service may or may not be available at any time. The availability is generally very good, but there are no guarantees. I have a life beyond this hobby, and sometimes it might take a priority.
3. If you choose to donate hardware, money, links, your time, or computing capacity to the aprs.fi service, you're not entitled to any additional rights, better service, or any service at all should the service become unavailable.
4. aprs.fi is not open source software. It is copyrighted. Learn from it, do not steal it. Some specific, smaller parts are separately published as open source.
5. You are not allowed to "frame in" content from the aprs.fi service, except as described on the embedding page.
6. You are not allowed to scrape content programmatically from the user interface of the aprs.fi service for the purpose of using it on another site or software application, except as described on the API page, or with a written permission from the maintainer of the aprs.fi service. In other words: You are not allowed to write software to download APRS data (messages, packets, positions or other data) from the aprs.fi web site or its internal APIs, except as described in the API document.
7. You are only allowed to crawl the site using a web crawling software for the purpose of providing a public and free-to-use web search engine service which links back to aprs.fi (such as Google or Yahoo).
8. The sole purpose of this site is to publish real-time and historical position tracking data. Such data is considered sensitive and private by many. If you do not wish to make your position known to everyone in the world, do not transmit it on the Internet or using APRS. If it gets to aprs.fi using the APRS-IS or other means, it will be published and retained on the service.
9. The service collects some other data too, such as your email address (if you choose to register it to create an account on aprs.fi). We will not intentionally sell your email addresses or phone number. But if the unlikely would happen, and they would be stolen from the service (using a physical or a virtual computer crime method), aprs.fi or it's maintainers assume no liability of any sort.
10. If it breaks, you get to keep both pieces. No refunds.

Please remember that, by law, you're generally only allowed to publish your own tracking data, and the position of your own vehicles, unless express permission from the target of the tracking is obtained.

Amateur radio transmissions are defined to be in the public domain (by FCC rules in the US, and by respective legislation in most other countries, and I suppose, by international regulations). Anyone can receive them, and retransmit, publish or store them as they wish. If you do not wish your position to be published on the Internet by someone, the only guaranteed way is not to transmit it.

Please take a look at the privacy policy, too. Thanks!