Few months ago critical and amazing vulnerability was discovered in mysql , you can see in detail here : by HD Moore ( founder of metasploit project ) , andCVE reference : http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-2122
mysql bug post : http://bugs.mysql.com/bug.php?id=64884
mysql bug post : http://bugs.mysql.com/bug.php?id=64884

RT @chris_kirsch: New: Free Scanner for MySQL Authentication Bypass CVE-2012-2122 lnkd.in/ZMMABf #ScanNow #Rapid7
— Rapid7 (@rapid7) September 20, 2012
Today rapid7 team released a tool to scan possible vulnerabilities in your network , that tool is free of cost and work on windows you can more detail and download link for tool in blog post .
if you already use metasploit framework or metasploit pro then you can use an auxiliary module to search in network for this vulnerability
msf > use auxiliary/scanner/mysql/mysql_authbypass_hashdump
use this tool to check and update mysql version is best way to prevent any attack