Participant attack on a kind of MQSS schemes based on entanglement swapping F. Z. Guo, S. J. Qin, F. Gao, S. Lin, Q. Y. Wen and F. C. Zhu Eur. Phys. J. D, 56 3 (2010) 445-448 Published online: 08 December 2009 DOI: 10.1140/epjd/e2009-00306-3