ZEBRAM is concerned with computer systems vulnerable to attacks exploiting the Rowhammer hardware vulnerability (present in all the modern main memory modules). Rowhammer is a security exploit that takes advantage of an unintended and undesirable side effect in dynamic random-access memory (DRAM), in which memory cells leak their charges due to disturbance errors, possibly changing the contents of nearby memory rows that were not addressed in the original memory access. ZebRAM is the first comprehensive open source software protection against all forms of Rowhammer, and it is based on a novel technique that uses guard rows as fast, memory-based swap space, significantly improving protection without sacrificing memory capacity compared to the state of the art.