var url:String = "http://cs610225.vk.com/upload.php?act=add_doc&mid=67296096&aid=0&gid=0&hash=9f947d7de2445d4595d9ff9e63b8b583&rhash=3cd41dc47965d7509196b89f99794380&api=1";

var ba:ByteArray = new ByteArray;
        ba.writeUTFBytes("Test блять на хуй");


        var fileContentType:String = 'text/plain';
            var mpLoader: MultipartURLLoader = new MultipartURLLoader();
            mpLoader.addEventListener(Event.COMPLETE, completeUpload);
            mpLoader.addFile(ba, "mytext.txt", "file", fileContentType);
            mpLoader.load(url);

/***************************/

{"file":"67296096|0|0|610225|53c845bd2c|txt|29|mytext.txt|daa21dc5ef5021f0bad4256790fc62c5|21f8172c28eaf10cf79dc3a97f1855aa|"}