uBlock Origin is NOT an “ad blocker”: it is a wide-spectrum blocker – which happens to be able to function as a mere “ad blocker”.
The default behavior of uBlock Origin when newly installed is to block ads, trackers and malware sites – through EasyList, EasyPrivacy, Peter Lowe’s ad/tracking/malware servers, various lists of malware sites, and uBlock Origin’s own filter lists.
uBlock Origin (or uBlock₀) is not an ad blocker; it’s a general-purpose blocker. uBlock₀ blocks ads through its support of the Adblock Plus filter syntax. uBlock₀ extends the syntax and is designed to work with custom rules and filters. Furthermore, advanced mode allows uBlock₀ to work in default-deny mode, which mode will cause all 3rd-party network requests to be blocked by default, unless allowed by the user.
That said, it’s important to note that using a blocker is NOT theft. Don’t fall for this creepy idea. The ultimate logical consequence of blocking = theft is the criminalisation of the inalienable right to privacy.
Ads, “unintrusive” or not, are just the visible portions of privacy-invading apparatus entering your browser when you visit most sites nowadays. uBlock₀’s main goal is to help users neutralize such privacy-invading apparatus — in a way that welcomes those users who don’t wish to use more technical, involved means (such as µMatrix).
EasyList, Peter Lowe’s Adservers, EasyPrivacy and Malware domains are enabled by default when you install uBlock₀. Many more lists are readily available to block trackers, analytics, and more. Hosts files are also supported.
Once you install uBlock₀, you may easily un-select any of the pre-selected filter lists if you think uBlock₀ blocks too much. For reference, Adblock Plus installs with only EasyList enabled by default.
Dynamic filtering: default deny
Default-deny is an awesome blocking mode for whoever agrees that in general most 3rd-party resources from web pages:
are not really all required
increase privacy exposure
Strictly speaking, default-deny means to block everything and let the user choose what should not be blocked. This strictest mode of default-deny is impractical though, as this means that most web pages would be broken, and more than likely most users would not make use if it.
With uBlock it is possible to use more relax (and thus practical) versions of default-deny: default-deny 3rd-party resources (stricter), or default-deny 3rd-party scripts/frames (more relax).