I recently looked at the tags for my WP site and saw dozens of tags which I didn't add, and which seemed unrelated to any posts I've ever made. Many of them looked like random dictionary words. A handful of them had descriptions and a google search for the exact description text brings up many sites with the exact same tags, e.g. "8bit", "Mothership", "Nailed It", etc.
My question: how and by whom where these tags added? Are they installed by default by some plugin? Are they evidence of a vulnerability?