I’m a PhD student at the Univ. of Colorado and I’m doing research on cloud computing and services. I am trying to understand some operational aspects of running a web service.
To some degree, I understand the clear malicious attacks and protections against them. My question is: what are some non-malicious activities coming from your users (who are using your service) that you have experienced that are annoying or even affected your service (e.g., a user sending malformed requests, overwhelming your resources)?

Did you have to do something about it (even pre-emptively), and if so what (blocking user? sending warning to users? etc)

Thanks a lot,