Louisistan, I think its because spam causes an increase in the amount of pages open which can intensify the frequency in which ads appear. As it appears to be less prevalent, I'll move it to 10000 Islands.
How is this issue now? For the most part, redirects should be auto detected and queued to be removed from the system. Proboards support advised me that this happens daily.
if you encounter the re-direct ads please provide: country, browser type, and OS.
Additionally, if a member encounters a redirect, use the browser's back button to return to the forum as this action helps the detection system. You can then spot which ad is active, report it using the report button and also alert me.