API Hammering is a trick can used to avoid being caught by security software. Imagine you're trying to hide what you're doing by doing a lot of pointless things at the same time. That's kind of what API Hammering does. It makes the computer do a bunch of unnecessary tasks, like opening and closing files or running empty loops, to cover up the real malware stuff it's trying to do.
This method helps these programs such as malwares stay hidden because security tools, which quickly scan what programs are doing, might just see the noise (all the useless tasks) and not the quiet, bad actions happening in between.
Each Functions are explained.
By @5mukx