These don't benefit us, the website users, in any way. In fact, they use a lot of our computing power and bandwidth against us.
Hands-down the best ad-blocking browser extension. It's free software (GPLv3), blazing fast, and will effectively block most malware. We heartily recommend that everyone installs it. uBlock is available for most browsers on Windows, MacOS and Linux. Install it now!
Note that other browser extensions, such as the popular "AdBlock", are unsafe: they have accepted money to expose you to some ads. Don't fall for it, just use uBlock Origin instead.
This is a DNS server that can block ads and trackers throughout the whole system. This includes video ads and ads in your favorite apps, browsers and games. It can be used as a replacement or, better, a complement of uBlock Origin.
An alternative to AdGuard for system-wide blocking is to directly manage your hosts file. Here's a list of dangerous hosts to block, with links to raw hosts files available. To modify your current hosts file, look for it in the following places and modify it with a text editor.