There have been a number of comment spam attacks in various posts in a couple of /c's that I follow by a user/individual who uses account names like Thulean*
For example: ThuleanSneed@lemmy.tf in !coffee@lemmy.world
and ThuleanPerspective2@eviltoast.org in !anime@ani.social
edit: Also ThuleanSneed@startrek.website in !startrek@startrek.website
The posts have been removed or deleted by the respective /c's mods, and the offending accounts banned, but you can see the traces of them in those /c's modlogs.
The comments consist of an all-caps string of words with profanities, and Simpsons memes.
An attack on a post may consist of several repeated or similar looking comments.
This looks like a bored teenager prank, but it may also be an organization testing Lemmy's systemic and collective defenses and ability to respond against spam and bot posts.
I'm not sure how extensive the spam wave was, nor how quickly the user was able to create an account, make the comments.
I doubt that the quantity in that I came across would be enough to take down a server, but that may be the point: To test lemmy's collective defenses and response without drawing too much attention.
A common IP address or address range ban file that's frequently updated and downloaded by each instance might be another way to boost security.
If this is actually an org attack, I'm guessing that we'll see botnet DDOS comment and post attacks next.