Correct answer:

Also known as a wart. This is a well-localized horny projection that is common on the fingers, hands, feet and knees, particularly of children and young adults. Crops of warts may occur on the genitalia and perianal region, in many cases spread by sexual contact. Warts are often multiple and are due to a number of different strains of human papilloma virus. Microscopically, there is a local hyperplasia of the prickle cell layer of the skin (acanthosis) with marked surface cornification.