Microprobing is one kind of physical attack that directly probes at signal wires in order to extract sensitive information. Successful microprobing attacks have been reported on smartcards and microcontrollers in mobile devices. In a successful microprobing attack, plaintexts such as personal data, code format intellectual property (IP), or even encryption keys can be compromised. Most security critical Integrated Circuits (ICs) are reinforced against microprobing attacks with active shields to detect a breach and zero-ize sensitive information once a breach has been detected. However, major problems exist with this approach. Active shields are designed to cover the entirety of the die, and in some designs more than one metal routing layer is required. This puts a prohibitively high cost on the design, and leaves ICs fabricated with technologies offering a smaller number of available routing layers dangerously exposed to microprobing attacks. Furthermore, research has shown that using active shields in the top metal layer of an IC is very ineffective against microprobing attacks.