Security on VPS
From Lunarpages Web Hosting Wiki
Is my web site more or less secure on a Virtual Private Server hosting account?
We maintain the security of the hardware node on the VPS plan. You need to be sure you don't run unneeded services on it and use secure passwords for accounts on the server, especially for the ones with admin privileges.
VPS and sites hosted on it also should run up to date software that does not contain known vulnerabilities. Meeting these conditions, your VPS will not be less secure than shared plans and even you can get it more secure as there are some things that can't be disabled on shared servers due to the nature of the shared hosting.