Copyright will protect your intellectual rights to your Flash file.  A copyright exclusively signs the rights to your animation or game directly to you, and lawfully attaches the file to your being.  For anyone to legally use the file, they would need to get written or expressed permission from you to use the file, even if its just the compiled swf file.

Here are some of the cases most exploited by those without copyright, which would now be protected:
Anyone who reverse engineers or decompiles your Flash file cannot distribute any part of the file outside their own computer, meaning that your file is not susceptible to modification+.  In addition, the Digital Millennium Copyright Act also requires the user to seek permission to decompile the file+.
  Anyone infringing on copyright will gain the ability to contact their Internet Service Provider (ISP) to reveal the identity and information of the user, in the case that further legal action will need to be reached+.  This means that no one can hide if they are stealing your file.
Websites located worldwide will need to ask you permission before using your file, and you can give them as much permission as you like.

Common internet myth suggests that that when you publish your work, it is automatically thrown into the copyright pool.  To some degrees, this is true.  You will gain all the benefits listed above for just making a physical copy of your work.  The 1976 Copyright act changed the publishing law to state that as long as you made a physical “copy” of the file, regardless of publishing or not, you have obtained copyright of your own file+.  But legally, you will lose a lot of protections that are guarenteed with copyright.

By obtaining a United States copyright, you will be legally protected in many ways if an infringement lawsuit goes to court.  First, you may not go to court for an infringement lawsuit unless the file is protected by United States Copyright.  Second, in the stance that your infringement lawsuit is won, your court and attorney fees would be covered.  And third, your copyrighted protection will confirm 100% that the flash file is yours in evidence.  Your opponent would need to justify why this isn’t the case, which makes a difficult case.

If people are committing infractions outside the United States, your file will be protected if the United States has a treaty with that country. That list can be found here. As seen on this link, the United States has a treaty with a majority of countries.

Your Ideas
The main goal of a copyright is to protect a project from copying.  Any part of the flash used in part or whole will be in violation of copyright by anyone you do not allow.  However, one important issue to take into consideration is the idea of using “ideas.”

You cannot copyright an idea for a game, or the gameplay itself.  The same applies for animation themes or issues.  Gameplay or story is an “idea”, something that is not protected by copyright.  So if you are copyrighting a game to protect a neat gameplay idea, it will not be protected.  If you are copyrighting to protect your file so that people won’t steal your neat gameplay code, which will be protected.

Can I copyright a name or logo?
The idea of copyright is not to copyright one’s name.  It is to copyright a body of work.  A single phrase is not enough to create copyrights for.  The same goes for any sort of title or domain name for your own personal website, which is each classified as not being bodies of work.  Your logo, if just a picture of your name, also will not qualify.  A mascot, however, will be protected if you choose to separately file a copyright for that character.

What Will I get? How long does it take?
The wait for getting confirmation on your copyright takes a long time. There are thousands of people getting copyrights all the time, so you must wait your turn. It will take anywhere from 3-6 months. You will get contacted if there are any issues with your form, and once everything is in order, you will get a copyright certificate from the Library of Congress, as well as a copy of your application.

How much does it cost?
The current cost is $45 USD.

Where do I start?
Flash Rights provides a step-by-step instruction service for getting a copyright four your flash. You can start by visiting the How to Get a Copyright page. Or, if you feel inclined to go straight to the forms, you can visiting the United States copyright office website, http://www.copyright.gov/. If you are from another country outside the United States, you should seek your local government's copyright office, usually located at their website.