These atypical cells with enlarged and hyperchromatic nuclei are indeed infected by a virus; however, the etiologic agent is a type of human polyomavirus known as BK virus rather than CMV suggested. Human polyomaviruses are a group of human papovaviruses. They are related to two famus viruses - JC virus that causes PML (progressive multifocal leukoencephalopathy) of the brain and spinal cord, and SV40 (simian virus 40) that is very oncogenic in experimenal animal models.
Like JC virus, BK virus is considered ubiquitous. A majority of human beings are exposed to these viruses early in life (evidenced by high incidence of positive serology in adults), but the virus is almost never completely cleared. Instead, they remain dormant in small copy numbers in selected tissue types (BK virun in urologic system, JC virus in central nervous system), and infection can be reactivated when the host is immunocompromised (iatrogenic immunosuppression in organ transplant recipients, chemotherapy-induced myelosuppression, HIV infection). The differential diagnosis is high grade urothelial dysplasia or urothelial carcinoma (including invasive and flat in situ carcinomas). For this reason, these cells have been nicknamed "decoy" cells. When diagnosed, patients with BK virus nephropathy (reduced renal function) should be managed accordingly - reduction of immunosuppressive therapy and/or antiviral therapy. More information on this entity can be found in the internet. For example, http://www.viracor.com/diagnostic-virals-bk_overview.htm.