What exactly is a DDoS attack?

In a DDoS attack so much traffic is sent to a server that it can no longer serve real visitors. Nothing is hacked: it is a deliberate traffic jam.

How it works

The traffic comes from many different devices at once, often infected computers. That is what makes blocking hard: there is no single source to shut off.

How to recognise it

Your site is unreachable or extremely slow, while the logs show enormous numbers of requests from varied addresses. Your visitor statistics show nothing, because those requests never reach your tracking code.

What helps

Filtering upstream of your server, before the traffic arrives. In practice that means your hosting provider or an upstream service has to handle it — on your own server you are already too late.

What does not help

Restarting, or a bigger server. That shifts the threshold without removing the problem.

What you prepare

Know who to call and how quickly that party responds. It is the only part you can arrange in advance.