Last night I noticed that a lot of my comments seemed to have random Vimeo video’s embedded into the comments. Sometimes one, some times many. At first you think somebody would use embedding Vimeo embedding code/tags to do so but it was very wide spread over many comments over the years.
So was I hacked? Nope. I did find no evidence of that and I also did not find any hidden code/tags. It turns out to be a Jetpack 3.9.5 bug and the fix was to either disable or get a new version of Jetpack that would fix the issue: Jetpack 3.9.5 and 3.9.6: Maintenance Releases
As 3.9.6 was available today I upgraded to that version to see if that would also fix this annoying issue.
After updating to Jetpack 3.9.6 the issue has indeed gone. Good news!