Malicious JavaScript code used to be contained in single .JS or .HTML files, which made malicious JavaScript analysis and detection pretty straightforward. However, in the past few days, a couple of distinct Web compromises caught my attention because the codes involved used the multipart malicious JavaScript technique. In this technique, malicious JavaScript codes can be divided into multiple parts to make up different files.

Continued here:
Increased Use of MultiPart Malicious JavaScripts in the Wild