Viruses may be a more limited problem on smartphones and tablets, but they do exist. So do antivirus apps for helping you deal with them. Do you use them?
Viruses for Android and iOS are not quite the problem they are for desktop operating systems, primarily because there's no real opportunity for self-replication. You actually have to install apps yourself and give them specific permissions. Apps also run sandboxed, so their interaction with other apps and the operating system itself is more restricted.