1. A computer-implemented method of hygiene-based determination of legitimacy of activities performed by applications on clients, the method comprising: receiving, from a client, information regarding an application that is performing an activity on the client; determining a score distribution for hygiene scores of other clients on which a same type of application has performed a same activity, the determining comprising: reviewing the hygiene scores of the other clients on which the same type of application has performed the same activity, the hygiene scores representing the other clients' propensities for being infected by malware; and determining, using the reviewed hygiene scores, a malware infection rate of the other clients relative to a malware infection rate of all clients, wherein the malware infection rate of the other clients being greater than the malware infection rate of all clients indicates that the activity performed by the application is likely malicious; correlating the activity being performed by the application on the client with the score distribution for hygiene scores of the other clients on which the same type of application has performed the same activity; computing, based on the correlation, a reputation score for the activity with respect to the application performing the activity; and identifying, based on the reputation score, whether the activity is an illegitimate activity for the application.