Most of these attacks are reflection attacks, meaning they are just exploring normal protocol behaviors. Meaning these machines, are not necessarily infected but are just innocent participants in the attack.
For example somebody has a Memcached instance running on a public machine and does not realize they have UDP ports on 11211.
The attack discussed in the blog post was an HTTP attack, so reflection and amplification were not involved. The attacking machines are most likely infected, and can be labeled and tracked.
For example somebody has a Memcached instance running on a public machine and does not realize they have UDP ports on 11211.
"Memcrashed - Major amplification attacks from UDP port 11211": https://blog.cloudflare.com/memcrashed-major-amplification-a...
Incompetent participants, but non notwithstanding still innocent.