The reliability of virtualization infrastructures in the face of availability issues is a long-standing problem. Current fault tolerance approaches such as live VM replication are effective at addressing external, accidental issues (e.g. hardware failures, power cuts, environmental disasters); however, against an active attacker exploiting zero-day denial-of-service (DoS) vulnerabilities in the hypervisor itself, these approaches do not address the root cause of said vulnerabilities, and therefore cannot protect against these issues. This is made more relevant by the prevalence of DoS vulnerabilities among many widely used hypervisors. We introduce heterogeneous replication, a new solution that enhances live VM replication so that VMs can be replicated across different hypervisors. We show that heterogeneous replication not only mitigates accidental failures from the external operational environment, but also mitigates DoS attacks arising from hypervisor vulnerabilities. We further show that heterogeneous replication can be used to increase the security of virtualized infrastructures without sacrificing availability. We build HERE, our implementation of the heterogeneous replication concept for replicating a protected VM across hypervisor boundaries. We describe the implementation of HERE, including details on the necessary VM state replications, as well as a dynamic checkpoint interval adjustment scheme that maximizes VM protection based on load levels. We evaluate HERE using various benchmarks to show that HERE meets the goal of protecting VMs from availability issues while adapting to the VM's computing load.