Is md5 can realy decrypted?

I know that md5 is not encryption but algorithm. So it can't be reversed.
But, some people claim that md5 can decrypted, like http://www.md5er.com/.

Somebody can give me a fever about this? 'cause this makes me confuse. :(

Thank you..

The short anwser is: No.

The claim of MD5 decoding involves databases of md5 values of common words or brute force using a dictionary of words. The web site at the link you posted is probably adding anything entered in the "encode" form to it's own database of MD5 values.

You can protect against anyone "decoding" your md5 values by appending a random/nonsense "salt" string to the actual string to be encoded, and then performing the md5. This will insure that your MD5 value won't be found in any of these MD5 databases.