We experienced a DDoS attack on 3 May. It took awhile to mitigate the attack and then it somehow caused an issue with both CDN companies we were using. We had to remove the CDNs, which necessitated changing the DNS settings for every site. Once those settings have propagated, the sites will be up and running again. Unfortunately, with the CDNs shut down, this may cause some issues with server load. We are looking into a paid option for a firewall/CDN service.