Keeping your computer systems clean of viruses & other problems is often one of the job responsibilities of IS, which also is usually only practical with a corporate security policy to discourage the kinds of activities that lead to later infections.
It is possible to keep viruses & other trouble off of many computer systems, but it takes work, and sometimes money. Many companies do not want to spend money on security or budget personnel time to avoid these problems.
Some old systems canget so badly messed up with viruses, that you are better off reinstalling the software & restoring to a backup that was made prior to the infection, assuming you have any idea when that was.
We either need to get a computer system which is immunefrom viruses ... I talk about that in my thread on Computer Security Education ... or we need to have high quality anti-virus protection that is relevant to the kind of hardware & software that we are using & we need to keep that protection up to date & we need to have daily backups.