This is recent enough that I never encountered it during my IT career. The word is listed in Wiktionary, which gives a few usage examples. The word can also be found in software development books like Fuzzing for Software Security Testing and Quality Assurance (2008), by Takanen, Demott and Miller.
Fuzzer will be accepted in future as a rare word. Fuzzing is already accepted, thanks to various verb senses of the word fuzz: to make or become fuzzy, etc.