Before anyone else starts ANOTHER thread about this, please realize that the UABB is already spearheading a legal and unbiased investigation into MyBitcoin.com but needs your support. Discussion about MyBitcoin.com is very healthy for the sharing of ideas and suggestions on how to tackle this very serious and difficult problem, but nothing will be done about it through forum posts.
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I don't think this is the appropriate answer to a technical question which has nothing to do with the previous MyBitcoin-Threads.
To actually answer the question: to my knowledge a once made transaction cannot be reversed even it's not yet redeemed.