So an attacker using a large number of high performance hosting in order to build a much larger botnet of for a DDOS attack. This attack is happening at a global level and WordPress instances across hosting providers are being targeted. Since the attack is highly distributed in nature (most of the IP's used are spoofed), it is very difficult to block all malicious data.
According to the statistics recently published by WP WhiteSecurity, more than 70% of WordPress installations are vulnerable to hackers out of the World's Top 1 Million websites having a Wordpress installed.
If you are running WordPress sites, now would be a good time to ensure that strong passwords are always used and that your username should be changed from "admin".
Avoid Obvious Passwords, Scan your computer for viruses, keyloggers, rootkits, and botnet software. Most importantly, Update WordPress and all plugins to the latest versions.