The internet has been slowed down all over the world after a huge cyber-attack on tech company Spamhaus.
Security company Arbor Networks said the attack is the biggest they have ever seen.
It is having an impact on popular services like Netflix.
How are websites attacked?
- The attacker gets hundreds of computers to visit a target website over and over again.
- Computers infected with a virus could be made to join in the attack - and the owner wouldn't know.
- The target website is overwhelmed by the amount of visits to the website and can't respond to them all.
- People who actually want to use the website find it is unavailable or responds very, very slowly.
- This is called Distributed Denial of Service attack - or DDoS for short.
Why has the whole internet slowed down?
The massive number of computers involved in the attack has slowed down the entire internet.
Security expert Professor Alan Woodward said: "Imagine the internet as a motorway."
"With this attack, there's so much traffic it's clogging up the motorway itself."