This paper surveys the security of the message integrity code used in the IEEE802.11 Wireless LANs. To address the security flaws of Wired Equivalent Privacy (WEP), the IEEE802.11i draft defines two data confidentiality and integrity protocols, Temporal Key Integrity Protocol (TKIP) and Counter-Mode-CBC-MAC Protocol (CCMP). TKIP is based on RC4, andCCMP is based on the AES cipher. TKIP includes a keyed hash functions, called Michael, as the messag integrity code. The aim of this paper is to summarise the recent research results of Michael and analyse the practicability of two attacks against Michael.