“The technique exploits the different methods ZIP parsers and archive managers handle concatenated .ZIP files.”
Glue two ZIP archives together and every tool sees a different file. 7-Zip reads only the first, benign archive. WinRAR shows both, AutoIt trojan included, and Windows Explorer either chokes or shows only the second. A security scanner that parses like 7-Zip waves the payload straight through to the user who opens it in WinRAR.