For a while if I went through Varrock west bank area I could guarantee getting at least a dozen PM spam messages within 5 minutes. I did take the time to report them. It may have been a useless exercise as they were probably throw away spam bots, but, I wanted Jagex to know in a small way that they were there. I also noted in the forums what I suspected. I believe there were bots in Varrock that harvested the names of players present and then send that list to a server somewhere and the spam bots were using that to spam us.
In the last week I believe Jagex did something as I have received zero PM spams! I visit Varrock west bank several times a day and nothing! I don't know what they did, but, thank you!
Now if they can do something about the spam bots in W301 advertising, there is so much spamming you can't see the messages from legit players advertising their stuff. Maybe the new market place coming up will help.
I am playing old school as it is still more fun than the shiny graphical RS. I may go back when I get bored, but, it just does not feel as fun as OSRS.