The crossword solution for the term 'Virus Prefix' is 'ANTI'. This prefix is commonly used to describe something that is against or opposed to something else. It is often used in medical terms to describe a substance that is designed to fight off a virus, such as an antiviral medication. In other contexts, it can be used to describe something that is intended to prevent or reduce the effects of a virus, such as an ANTI-virus software program.