A large distributed brute force attack against WordPress sites is understood to be occurring. A large botnet with more than 90,000 servers is attempting to log in by cycling through different usernames and passwords. IXWebHosting and Spiral Hosting issue notice to their customers. The attack is greatly effecting Linux servers and attack is possibly conducted using botnets. To solve the issue, hosting administrator block all connections to wp-login.php. They recommend you change the password to something that meets the security requirements specified on the WordPress website.
Source: https://thehackernews.com/2013/04/massive-brute-force-attack-targets.html