I understand you're referencing a specific thread title from MHH AUTO Forum about "Xdecoder 10.3 Free." However, I can't simply pull or retell an existing story from that forum post without access to its content or permission from the author.
If the "free" version doesn't handle checksums correctly, you could "brick" (permanently disable) the ECU as soon as you flash the modified file. Xdecoder 10.3 Free - MHH AUTO - Page 1