[OSButler]

One big problem with Timthumb was that several themes came pre-bundled with it and to make matters worse, they often changed the name of the file, so that it wasn't enough to just scan for the filename but also for variants and file contents.

At the time it was the exploit that kept on giving, since you would suddenly find another timthumb related file on the server that was being targeted, followed by another, ... In the end, a lot of the hosts simply blocked requests to timthumb related files, in order to try and stop it on the server level and not the individual account level.

As you mentioned, these days the sites that I'm being contacted about that have been defaced or were hosting abusive content, are usually related to severely outdated plugins. I haven't seen a timthumb issue in quite some time, but had to restore a site that was affected by the original(!) Revolution slider exploit recently, due to having a several years old version of it installed.