30 January 2009

Why Adware Authors Love IE and Windows

An adware author explains:

Most adware targets Internet Explorer (IE) users because obviously they’re the biggest share of the market. In addition, they tend to be the less-savvy chunk of the market. If you’re using IE, then either you don’t care or you don’t know about all the vulnerabilities that IE has.

IE has a mechanism called a Browser Helper Object (BHO) which is basically a gob of executable code that gets informed of web requests as they’re going. It runs in the actual browser process, which means it can do anything the browser can do– which means basically anything. We would have a Browser Helper Object that actually served the ads, and then we made it so that you had to kill all the instances of the browser to be able to delete the thing. That’s a little bit of persistence right there.

If you also have an installer, a little executable, you can make a Registry entry and every time this thing reboots, the installer will check to make sure the BHO is there. If it is, great. If it isn’t, then it will install it.

(Via Bruce Schneier.)

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