Last year, Chrome started to block downloads for applications that "make unexpected changes to your computer — for instance, switching your homepage or other browser settings to ones you don't want". Now Chrome shows a warning when you visit a site that "encourages downloads of unwanted software".
Here's the warning page: "The site ahead contains harmful programs. Attackers on example.com might attempt to trick you into installing programs that harm your browsing experience (for example, by changing your homepage or showing extra ads on sites you visit)". This is a new SafeBrowsing feature, just like malware and phishing warnings, and you can disable it from the settings.
In addition to displaying Chrome warnings, Google will also downrank search results and disable Google ads that lead to sites with unwanted software.
There's a Google page that provides more details about unwanted software. According to Google, unwanted software has at least one of these characteristics: it's deceptive, it affects the user's system in unexpected ways, it's difficult to remove, it collects or transmits private information without the user’s knowledge, it's bundled with other software and its presence is not disclosed.
