As part of the devs farewell message on their site, they have included malicious code to make each visitor sends 2,000 requests to the dbzer0 servers in an attempt to DDOS and take the instance offline.
I don't have a link or full context, but it turned out that the dev of tessaract (open source program for fediverse sites, involving at least spam and blocking tools) had a functionality in the program that fetched their own block list from their site. But this blocksite was blocking a huge amount of users, fediverse domains, and anything with any keywords which would be anything political, some porn/sexual terms like Yuri, and lots more. This block was completely invisible the ones running the program and would also give fediverse instances that were blocked a generic failed to connect error instead of saying blocked, preventing the fediverse instances from talking.
Seeing the above, it seems like the dev didn't handle this discovery in any good way either and retaliated but doing this ddos thing.