Virus Scanner companies have engineers who develop the virus scanning software. I myself have not worked on any projects that work with viruses. However, I am sure the teams of engineers vary in their specific engineering background but primarily consist of software engineers. As far as creating viruses there may be certain situations where software engineers may want to create a virus to simulate how secure their product is or how well their scanner may detect a specific type of virus.
There may be another engineer girl who is able to give a more specific answer. You may also try to email a person who works for a virus scanner company and let them know that you are interested in this area and ask if they can give you some information about their company and the type of work their engineers do. Engineers typically love to encourage new and young engineers who are interested in their field.
I hope I have helped, let me know if you have any more questions and even if I can't answer them I can hopefully point you in the right direction. Good luck and best wishes.