.net code injection
.NET Internals and Code Injection
http://www.ntcore.com/files/netint_injection.htm
Windows Hooks in the .NET Framework
http://msdn.microsoft.com/en-us/magazine/cc188966.aspx#S6
Rewrite MSIL Code on the Fly with the .NET Framework Profiling API
http://msdn.microsoft.com/en-us/magazine/cc188743.aspx
CLR Injection: Runtime Method Replacer
http://www.codeproject.com/Articles/37549/CLR-Injection-Runtime-Method-Replacer
.NET Framework Rootkits: Backdoors inside your
Framework