At least three anti-spam blocklists were taken down this week by Distributed Denial of Service (DDoS) attacks: Spamhaus, CBL, and APEWS. The first two are back up; the third is not.
The Composite Blocking List (CBL) currently has this at the top of its home page:
Important Information on Spamhaus/CBL DDOS
Commencing March 19 the CBL was hit by a very large-scale distributed denial of service attack. At the time of writing (March 21, 00:15 UTC) this attack is still ongoing.
Throughout this period the CBL DNSBL has continued to remain available through the CBL mirrors and via Spamhaus XBL (and Zen), and we've been doing our utmost to restore the rest.
Access to the lookup/removal page has just been restored.
The CBL rsync facility has been restored.
Email to the CBL is not working yet.
We ask for your patience while we finish restoring the rest of the CBL to service.
SpamRankings.net is receiving CBL data normally again, although yesterday's is lost.
We never saw any interruption in data from the Passive Spam Block List (PSBL).