Man in the Browser is a new breed of attacks whose primary objective is to spy on browser sessions (mostly banking) and in that process intercept and modify the web page contents transparently in the background. In a classic MITB attack, it s very likely that what the user is seeing on his/her browser window is not something which the actual server sent. Similarly, what the server sees on the other end might not be what user was intending to send. Why MITB? How different is it from conventional browser hijacking?
Source: https://threatpost.com/man-browser-inside-zeus-trojan-021910/73568/