With the increasing price so many fake ANN threads getting opened up. Probably threads filled up with viruses, fake pages.
Simple : Use the Report to Moderator button and if the thread is spammy/contains a virus, they will be trashed by the mods.
To discourage such movement, I ask miners to be more vigilant and;
Miners have nothing to do with the threads on bitcointalk? Are you confusing the members here with miners? Don't worry miners are not remotely associated with these useless threads.