The site adjusted the spam filters (I don't know the technical details) and that prevented most of them. These new attacks by spambots were accounts that were created on the site more than a year or two ago, and had been laying dormant. Until a few days ago, when they rose like zombies and flooded the board with spam PMs.
We deleted most of them, but there might still be residual crap left...like
@Ellocohombre said, please report them, especially if they do not have a line through their handles (which means they were already deleted). Thanks.