content: I was about to quote the exact same paragraph. Actually, there is malware that behaves exactly like that: replacing the normal ads with ads by the attacker which gives them nice revenue. After all, there were ads anyway so it's not directly apparent to the user. How out of your mind do you have to be to knowingly install malware on your system? But I guess not many people were that stupid. In scale of the Internet some 50,000 users are close to nothing.