With proper precautions, systems can be secured properly and with quite good security. Anytime a computer doesn't have encrypted data it's insecure, assuming an attacked has physical access. Installing a new operating system while keeping old data is cake. If a laptop is stolen or attempted to access data that is encrypted with proper security measures, it's pretty tough to break. Nothing is ever 100% secure but with proper security measures and encryption (either full disk or of sensitive data) it's pretty tough.