I have a website with an average hourly homepage visit of ~150, however, in the last day it suddenly jumped up to over 1000 visits per hour. Only the homepage is visited. How to determine what is causing the activity and should I be concerned?
Your server log files should have detailed info on where hits are coming from. If you are using Apache, it keeps such logs in a "access.log" file, often in paths like "/var/log/apache2/access.log". (Though the exact location depends on the system and setup method.)