From the Internet Archive Blog:

The Internet Archive is “currently in its third day of warding off an intermittent DDoS cyber-attack,” writes Chris Freeland, Director of Library Services at Internet Archive. While library staff stress that the archives are safe, access to its services are affected, including the Wayback Machine. From the post: 

Since the attacks began on Sunday, the DDoS intrusion has been launching tens of thousands of fake information requests per second. The source of the attack is unknown. “Thankfully the collections are safe, but we are sorry that the denial-of-service attack has knocked us offline intermittently during these last three days,” explained Brewster Kahle, founder and digital librarian of the Internet Archive. “With the support from others and the hard work of staff we are hardening our defenses to provide more reliable access to our library. What is new is this attack has been sustained, impactful, targeted, adaptive, and importantly, mean.” Cyber-attacks are increasingly frequent against libraries and other knowledge institutions, with the British Library, the Solano County Public Library (California), the Berlin Natural History Museum, and Ontario’s London Public Library all being recent victims.