Mods can't win a war against machines (aka bots).
Even if they focus on the section of the forum, bots will change the section of the forum and the spam will start again, we need a restriction on the start of the problem and not on the end.
But the sole purpose of mods is to supervise the section/board that they are assigned to, am I right?
Yes, supervising these bots are such a tedious tasks but that is one of the responsibilities of the mods and we must encourage them to fulfill their responsibilities (even though it is very difficult, but possible).
Moreover, each one of us can report these bots by using the "report to moderator" function. By doing so, we can lessen the burden on the mods.