I think it is possible to do a delete batch to suppress all these messages . I have not found any sample query *, such as :
delete from forum_posts where subject like "%word1%" AND subject like "%word2%" AND created = "(creation date here)"
The question can be related to this now closed discussion :
- Fighting spam on moodle.org
* Custom SQL queries
By the way, the Moodle doc about forum tables is not detailed in :
- Moodle Database structure
(sorry I do not have time to edit the wiki content and add a longer description of the 8 forum tables with a link from this schema introduction page...)