Recently did the E4 infa onsite, with all the other posts about what leetcode questions there are a ton good posts out there, and I wouldnt be adding anything new so I will be skipping those. I was lucky and able to solve all coding questions there was nothing I saw that I hadn't already seen (At 400+ leetcode right now) but I got a System Design question that I had never seen anyone talk about, I did all my prepping for questions like Design ticketmaster, Design youtube, Design a distributed cache. Etc all the common questions Ive found in the discuss section. But I was given a question I was completely unprepared for. My interviewer asked me to design some software that could hack a website (Messenger) and read all messages / pages undetected. I had not studied this and had no idea how to answer. I started with functional and non functinal requirments much like I had practiced but the interviewer stopped me and said that wasnt important. The things I remember he wanted to hear was talking about different authentication types. Spoofing these, and to intercept messages and pages while remaining undetected. And decodeing encryption / hashing. Needless to say I don't think I even got a working system for this question. I was rejected and was able to setup a call with my recruiter and prey about feedback, she caved and told me some specifics from my packet, and she said that my coding rounds were perfect, had good working code, clear communication, but based on my system design performance they felt I was not ready for the role and to try again in a year. So some things to note, the system design aspect is just as important as coding, make sure at the bare minimum you have a working system. And in addition to questions like Design ticketmaster, twitter, live comments etc be prepared for curveball questions and make sure you also study Authentication, spoofing, decoding algorithms, how encrypting and hashing works.