In the paper [Phys. Rev. A \textbf{69}, 052319 (2004)], a quantum direct communication protocol is proposed which is claimed to be unconditionally secure even for the case of a noisy channel. We show that this is not the case by giving an undetectable attack scheme.
@article{arxiv.quant-ph/0406115,
title = {Comment on "Secure direct communication with a quantum one-time pad"},
author = {H. Hoffmann and K. Bostroem and T. Felbinger},
journal= {arXiv preprint arXiv:quant-ph/0406115},
year = {2009}
}