The high error rate of viral polymerases allows viruses to rapidly adapt to a new host, and each replication cycle results in a heterogeneous population of viruses with distinct genetic content. Routh et al. used an unbiased next-generation sequencing approach to look at the total RNA content of a purified non-enveloped single-stranded RNA virus, Flock House virus (FHV). They showed that, as well as the FHV genome, FHV virions contain a range of host RNAs that account for 1% of the total packaged nucleic acid and include mRNAs, ribosomal RNAs, non-coding RNAs and transposable elements. Such a high incidence of these host RNAs suggests that viruses such as FHV have an important role in horizontal gene transfer. Moreover, the authors found that host RNAs, including transposable elements, are also regularly packaged in virus-like particles (VLPs), which must be taken into account when considering the potential use of VLPs as vehicles for delivering gene therapy.