This new threat requires the popular Japanese archive utility Lhaca to be installed in order to associate the extension and capitalize on the vulnerability.  This may be need to be added to the blocking lists where it is pertinent. 

LhDropper - uses LHZ archive file extension
http://www.symantec.com/enterprise/security_response/weblog/2007/06/beware_of_lzh.html
http://www.symantec.com/enterprise/security_response/writeup.jsp?docid=2007-062506-5500-99

QUOTE: Trojan.Lhdropper is a Trojan horse that drops malicious files by exploiting a vulnerability in Lhaca, a freeware application that can compress and decompress LZH archive files.