This article was originally published as part of the Pobox blog. Pobox was acquired by Fastmail in 2015.

This morning, Pobox mail saw processing and forwarding delays. Most messages were delayed no more than 10 or 20 minutes, but we did get reports of a few messages taking an hour or more to be delivered to their final destination. In general, we try to keep delays for your mail to under 5 minutes; most messages are handled within seconds.

Today's delay was caused by a huge surge in traffic, that we've actually been dealing with for over a week, from a botnet. Botnets are massive numbers of computers (also known as zombies), typically people's virus-infected home computers, controlled by remote software for nefarious purposes. Some estimates say as many as one in 4 personal computers connected to the Internet are running botnet software.

This software can be used for different purposes. In our case, the botnet is being used to send spam. They are also commonly used for denial-of-service attacks, where huge amounts of traffic are targeted at servers or a company, with the goal of effectively blocking all legitimate traffic; or behind phishing attacks, where credit card or bank information is collected.

We are making a number of network and security changes to deal with this ongoing attack. There will be a series of brief outages this evening for the website, webmail, outbound SMTP and POP3/IMAP services, as we make upgrades and networking changes to prevent further delays.

Running a PC at home? Make sure that you have up-to-date anti-virus software, and run it regularly. Using a home firewall is also a good preventative step from keeping your computer from being used as part of a botnet. If you're running a Mac, you're probably safe. Thus far, there seems to have only been one Mac botnet, and it came from people downloading "shared" copies of iWork '09 and Photoshop CS4.