According to an advisory from maintainers of the open-source blog software, WordPress 2.6.2 was released on September 8 to mitigate a new attack vector discovered by PHP security guru Stefan Esser.
From the announcement:
Stefan Esser recently warned developers of the dangers of SQL Column Truncation and the weakness of mt_rand(). With his help we worked around these problems and are now releasing WordPress 2.6.2. If you allow open registration on your blog, you should definitely upgrade. With open registration enabled, it is possible in WordPress versions 2.6.1 and earlier to craft a username such that it will allow resetting another user's password to a randomly generated password. The randomly generated password is not disclosed to the attacker, so this problem by itself is annoying but not a security exploit. However, this attack coupled with a weakness in the random number seeding in mt_rand() could be used to predict the randomly generated password.