Since I changed from Google Analytics to Statcounter for my homepage I noticed via SC that almost all of my homepage visits were entering the site via example.com, not www.example.com.
at first I didn't get what this meant. But the other day I clicked on the example.com link in the SC entry page list and it took me to my site as example.com. It should have redirected to www.example.com.
Somehow the redirect in my htaccess had stopped working after several years of working just fine.
No idea how that happened.
But I had noticed when I visit WMT that G was showing me as owning two sites, example.com and www.example.com. I didn't think much about that, but if I recall right, that started showing up about the same time as the rogue traffic.
No idea if there is any connection, but I thought I'd mention it.
(I reloaded my htaccess file and it's working fine again)