How to detect and block viruses?

Does anyone know how to prevent the download of viruses and bots to my computer? I know my downloads are not the cleanest but they are nessicary. Is there a program i can use that would unbind viruses from my desirered downloads? My computer does detect viruses on some downloads but it obviously does not give me the option to delete the virus and save the file it only wants me to delete the downloaded material. Once again these downloads are nesicary, thanks for any tips and sorry for any typos as i am still not used to the itouch keypad.