Safebrowsing uses a privacy preserving hash prefix algorithm to match against urls.[1] 1 - The first 4 bytes of all url hashes in the blocklist are cached in t

Safebrowsing uses a privacy preserving hash prefix algorithm to match against urls.[1] 1 - The first 4 bytes of all url hashes in the blocklist are cached in the browser. 2 - When there is a match, you request of Google the actual urls on the blocklist. 3 - Client side your browser blocks loading the url. Google only knows that the site had a hash collision with the first 4 bytes of something in the blocklist. I, personally, think that's a fair price for otherwise free malware protection. It's also built into Firefox and on by default. [2] [1] https://developers.google.com/safe-browsing/v4#update-api-v4 https://developers.google.com/safe-browsing/v4#update-api-v4 [2] https://wiki.mozilla.org/Security/Safe_Browsing https://wiki.mozilla.org/Security/Safe_Browsing