We've been the target of distributed denial of service attacks on a couple occasions in the past week.
We just experienced an attack at around 12:22 PM today. We contacted our upstream carrier and had the attack mitigated by 12:26 PM.
For folks who are interested in what these attacks are, here is a link. They are relatively easy to mitigate once we've identified the target, but can cause momentary inconvenience while we work to identify the problem.