A lot has already been said and written about a vulnerability affecting all major implementations of DNS resolvers, discovered by Dan Kaminsky.
This post is just a reminder that you should apply patches relevant to your DNS server implementation as soon as possible. There are already several publicly available exploits and some indications that attacks are already happening.
For more information about the vulnerability and possible news on attack it is advisable to follow SANS ISC handler’s diary.
If you are unsure whether your DNS server is vulnerable to this particular cache poisoning attack there are several sites, such as this one, that can be used to assess your systems.