The other day I was troubleshooting 100% CPU utilization on a SQL Server 2008 database server. The server had 100 or so databases of varying sizes however none were larger than a few hundred MB and each database had a corresponding web site on a separate web server. Since the server hosted quite a few databases the high CPU needed to be resolved quickly because it was causing issues for everyone. High CPU on a database server can often be symptomatic of a issues occurring outside the server. In this case the real issue was in fact being caused by a SQL Injection attack on a web server.
Source : Solving SQL Server High CPU with IIS Request Filtering | Peter Viola
