while it might seem valuable to know what versions someone was running, in the end its useless information
Because so many upgrades end up not being complete.. as evidenced by the hundreds of posts on here where someone missed upgrading a file, etc.. Ideally, someone is going to have all 2.5 files, or all 2.3.3 files, or .. or .. but some dont.
Next, because someone discovers something running 2.5, or 2.3.3 doesnt necessarily mean that that version is insecure. It may very well mean that the owner upgraded from a version that had been previously exploited, but didnt know ..
I have working examples. A previously exploited site that I set up logging on ..They had been running 2.1 something or 2.2 (I dont reme which). We upgraded them to 2.3.3, changing the only admin password in the process. It took only a matter of an hour or so, before said exploiter came back and tried to "insert content" into a post. Failing to do so, they immediately attempted an old, but very public SQL exploit that had been used to get the admin password. That didnt work either, obviously, since they were no longer running the older exploitable version.
In other words, they already had the admin password from the blog being previously exploitable. They were going to be able to continue exploiting, until the password was changed. There was also no telling how long that previous admin password had been compromised, but it had probably been so for a while.
Had it NOT been for the logging of all of this, and had the password not been changed, it would have outwardly have appeared as if 2.3.3 was vulnerable.
The other factor is the PHP rootshell aspect of this. A good deal of people simply dont pay attention to the files to realize immediately when a rootshell was uploaded.
Tack on insecure plugins..
Tack on using other insecure web apps that dont get upgraded -- joomla, coppermine, and gallery come to mind immediately in that regard.
Is this particular hack something that has been fixed in WP 2.5?
You make a miguided assumption in that question. Nothing indicates that 2.3.3 is, prima facea, insecure. Therefore, it follows that there is nothing to fix in 2.5.
if you are paranoid, set up logging. Watch what happens to your blog.
-- Lastly, as an addendum, ro8kfbsmag.txt is a PHP rootshell. left unnoticed on ANY web site, it does not matter what version of anything someone is using. Called directly, the file provides access to just about any shell command (atleast those that PHP has access to). You could have fort fricken knox installed and they would still have a way in. Well thats not entirely true, but you get the idea.