Strange spam attack

[Domiav]

Hello guys;
we are experiencing a pretty strange kind of spam that involves revival of old discussions copying and paste part of a post.
No links, no adv text, no adv banners, no profile editing with urls into user fields or signature...nothing! just old th revival copying and paste a section of them-.-
Spam is made every time with a new user also if we don't ban the previous one, and every time it revive just a single discussion with a single post.
We have human verification on with logical phrases that require human presence without math quetsion like "the result of 2+2",we are asking color of logo and similar things with the answer that must be in italian(!).
Any help on this?
Thanks!