They made access to popular websites, such as Reddit, Twitter, Spotify and many other sites, intermittent.
Security experts said easy-to-guess default passwords, used on Xiongmai webcams, aided the hijacking.
The web attack enrolled thousands of devices that make up the internet of things - smart devices used to oversee homes and which can be controlled remotely.
In a statement, Hangzhou Xiongmai said hackers were able to take over the cameras because users had not changed the devices' default passwords.
Xiongmai rejected suggestions that its webcams made up the bulk of the devices used in the attacks.
"Security issues are a problem facing all mankind," it said. "Since industry giants have experienced them, Xiongmai is not afraid to experience them once, too."