Spam protection at sign up

[martinzlocha]

Detailed Description

Limit the number of times someone can signup from a given IP within a short period of time. If the limit is exceeded the user should be notified/silently ignored.

Context

This will prevent malicious users from using the website to spam others.

Possible Implementation

Store IP addresses and usernames of students which signed up recently and cross check when a new request is received. Remove information after several minutes to prevent from infinite growth of data. Kept in memory and not in the database to improve performance.