We focus our research on the APOBEC3 enzymes. These proteins are cytidine deaminases restricting viruses by introducing C-to-T mutations. These proteins can also ‘misbehave’ and incidentally mutate the cellular genome. We combine in silico, in vitro and in vivo approaches to determine: i. which viruses trigger APOBEC3 expression, ii. how viruses can evade APOBEC3 restriction, iii. under which circumstances the APOBEC3 proteins can incorrectly access and edit the cellular genome.