Facebook has reversed — at least temporarily — the quick and quiet change it made to its terms-of-service agreement that broadened its licensing powers over the Web site's user-posted material.

But Facebook is just the tip of the iceberg. When was the last time you read one of those ubiquitous "TOS" agreements from top to bottom? Do you know what you've agreed to?

Most Web sites do not announce changes in terms of service, and most Facebook users didn't realize until about a week afterward that members could no longer take their content with them when they closed their account on the social-networking site.

The new terms, until Facebook reversed them, had usurped their power and given the site itself the rights to maintain user-uploaded content — and the licensing to sell that content to outside parties.

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"Companies get into trouble when they try to move that content beyond the four corners of their service — that's what Facebook tried to do — and use content for commercial exploits," said James R. Marsh, a lawyer who writes ChildLaw Blog, which first posted news of Facebook's TOS change late last month.

In the extreme, he said, "They can take little Susie's pictures on the beach to Playboy, who then has their own license for using it — and you may not even know it. And then what? You're institutionalizing child pornography."

Most of us click right through the legalese of service agreements to get to, say, the iTunes Store, without stopping to read the fine print — and we are bound by the terms of the site the moment we start using it.

It's hard to know exactly what we've agreed to, and we agree to something almost every time we click a mouse.

"At the bottom of pretty much every page there is a terms-of-service [agreement] that tells you rules of the road in terms of that Web site," said Martin H. Samson, a New York attorney who runs the Internet Law Library, an online Internet law database.

Samson said he advises his clients to post changes to terms-of-use or service agreements without notifying the users of the site to the changes.

"Giving notice is a very difficult thing, so we will advise clients to say, 'If you want to see changes to terms of service, you'll have to come here and look.' I can understand why companies wouldn't want to try and reach out to millions of users to notify everyone. It's a logistical nightmare," Samson said.

Both Marsh and Samson recommend vigilance.

"In this day and age reading may be a lost art, but your failure to practice it may cost you dearly," Samson said.

There are many sites with draconian or absurd-sounding stipulations, and it's best to know what they are — and who is trying to profit off your photos and information.

Here are some terms-of-service agreements you may have already agreed to:

Gmail: "Google reserves the right (but shall have no obligation) to pre-screen, review, flag, filter, modify, refuse or remove any or all Content from any Service."

LinkedIn: "You do not have to submit anything to us, but if you choose to submit something (including any User generated content, ideas, concepts, techniques and data), you must grant, and you actually grant by concluding this Agreement, a nonexclusive, irrevocable, worldwide, perpetual, unlimited, assignable, sublicenseable, fully paid up and royalty free right to us to copy, prepare derivative works of, improve, distribute, publish, remove, retain, add, and use and commercialize, in any way now known or in the future discovered, anything that you submit to us, without any further consent, notice and/or compensation to you or to any third parties.

"You have to indemnify us and hold us harmless from any damages, losses and costs (including, but not limited to, reasonable attorneys' fees) related to third party claims, charges or investigations, caused by (a) your failure to comply with this Agreement, including, without limitation, your submission of content that violates third party rights or applicable laws, (b) any content you submit to LinkedIn or (c) any activity in which you engage on or through the LinkedIn."

Included in LinkedIn's mile-long list of user "DON'T'S": "Access, reload or 'refresh' or make any other request to transactional servers more than once during any three second interval.

"Adds to a content field content that is not intended for such field (i.e. submitting a telephone number in the "title" or any other field)."

Monster.com: You give up the rights to your resume when you post it on the job-hunting site:

"You understand and acknowledge that you have no ownership rights in your MyMonster Account, and that if you cancel your MyMonster Account, all your account information from Monster, including resumes, Profiles, cover letters, network contacts, saved jobs, questionnaires and email mailing lists, will be marked as deleted in Monster's databases and will be removed from any public area of the Monster Sites. Information may continue to be available for some period of time because of delays in propagating such deletion through Monster's web servers. In addition, third parties may retain cached copies of your Information."

Apple iTunes: If you're an American, you can't legally use or access the iTunes Store or AppStore from outside the United States (other countries have similar rules):

"U.S. ONLY. The Service is available to you only in the United States and is not available in any other location. You agree not to use or attempt to use the Service from outside of the available territory. Apple may use technologies to verify such compliance."

YouTube will hold on to your videos forever, even if you delete them from the site:

"For clarity, you retain all of your ownership rights in your User Submissions. However, by submitting User Submissions to YouTube, you hereby grant YouTube a worldwide, non-exclusive, royalty-free, sublicenseable and transferable license to use, reproduce, distribute, prepare derivative works of, display, and perform the User Submissions in connection with the YouTube Website and YouTube's (and its successors' and affiliates') business, including without limitation for promoting and redistributing part or all of the YouTube Website (and derivative works thereof) in any media formats and through any media channels. You also hereby grant each user of the YouTube Website a non-exclusive license to access your User Submissions through the Website, and to use, reproduce, distribute, display and perform such User Submissions as permitted through the functionality of the Website and under these Terms of Service. The above licenses granted by you in User Videos terminate within a commercially reasonable time after you remove or delete your User Videos from the YouTube Website. You understand and agree, however, that YouTube may retain, but not display, distribute, or perform, server copies of User Submissions that have been removed or deleted."

AOL Instant Messenger: "You may use AIM Products for lawful purposes only. You may not post on or transmit through community areas (e.g., message boards, chat, e-mail, calendars, instant messaging products) or other means any material that (1) violates or infringes in any way upon the rights of others, (2) is unlawful, threatening, abusive, defamatory, invasive of privacy or publicity rights, vulgar, obscene, profane, indecent or otherwise objectionable...."

And AOL owns everything you post in public places — and it can pass on your information to as many companies it wants without letting you know:

"You or the owner of the Content retain ownership of all right, title and interest in Content that you post to public areas of any AIM Product. However, by submitting or posting Content to public areas of AIM Products (for example, posting a message on a message board or submitting your picture for the "Rate-A-Buddy" feature), you grant AOL, its parent, affiliates, subsidiaries, assigns, agents and licensees the irrevocable, perpetual, worldwide right to reproduce, display, perform, distribute, adapt and promote this Content in any medium. Once you submit or post Content to any public area on an AIM Product, AOL does not need to give you any further right to inspect or approve uses of such Content or to compensate you for any such uses."

Microsoft Windows Live: WindowsLive's Code of Conduct applies to most of MSN's content-sharing services, including all of those new 'network' and 'profile' pages that pop up when you sign onto Hotmail:

"You will not upload, post, transmit, transfer, distribute or facilitate distribution of any content (including text, images, sound, video, data, information or software) or otherwise use the service in a way that:

"Depicts nudity of any sort including full or partial human nudity or nudity in non-human forms such as cartoons, fantasy art or manga.

"Incites, advocates, or expresses pornography, obscenity, vulgarity, profanity, hatred, bigotry, racism, or gratuitous violence.

"Promotes or otherwise facilitates the purchase and sale of ammunition or firearms."

"Microsoft reserves the right at all times to disclose any information as Microsoft deems necessary to satisfy any applicable law, regulation, legal process or governmental request, or to edit, refuse to post or to remove any information or materials, in whole or in part, in Microsoft's sole discretion."

Yahoo: You agree to not use the Yahoo! Services to:

"Upload, post, email, transmit or otherwise make available any Content that is unlawful, harmful, threatening, abusive, harassing, tortuous, defamatory, vulgar, obscene, libelous, invasive of another's privacy, hateful, or racially, ethnically or otherwise objectionable...."

Yahoo Video: "You retain ownership to Your Content that You submit for inclusion into the Service. However, by submitting Your Content to Yahoo!, You hereby grant Yahoo! and its affiliates the following worldwide, royalty-free, non-exclusive, sublicensable and transferable rights and licenses:

"To host, cache, store, archive, index, crawl, create algorithms based on, modify or transcode Your Content to appropriate media formats, standards or mediums as part of the Service;

"To use, distribute, reproduce, modify, remix, excerpt, adapt, prepare derivative works and compilations of, publicly perform and publicly display Your Content on the Service, on any Yahoo! property or in connection with any distribution or syndication arrangement thereof with third parties or third-party sites, in any media format or medium and through any media channels; and c. to use Your Content for and in connection with advertising, promotional or commercial purposes, including without limitation, the right to publicly display, perform, reproduce and distribute Your Content in any media format or medium and through any media channels."

Snapfish, the photo-sharing network, doesn't have to remove your photos just because you've asked it to:

"If you request cancellation of your account, Snapfish may (but is not required to) remove any and all content (photos) or other personal information from the Snapfish site, and your photos may not be accessible to you even if you choose to rejoin or reactivate your account at a later date. Information necessary for the purposes of maintaining business records regarding a cancelled account, including records of credit transactions and account ownership, will be retained in accordance with applicable law."

Tumblr: You can get booted for bullying:

"The blogging site just updated its content policy by tacking on a harassment clause—and put a freeze on the accounts of five mean members."

Verizon Fios says no to porn:

"They'll pull the plug if they catch you using their service "in a manner that is obscene, sexually explicit, cruel or racist in nature or which espouses, promotes or incites bigotry, hatred or racism."