Keeping business separate from personal
As of now I have two computers. One for my business and another for all other applications.
The business computer is way over due for an upgrade. I just purchased the software to upgrade, that too was long over due.

Someone told me that instead of buying a new PC for the business, to just buy an external hard drive.
My personal computer has internet access and the upgrade for the business software could also utilize the internet. As it stands now, the old business computer does not have access.

First, I do not know much about external hard drives. Are they portable or expensive?
Will access to the internet compromise the safety of my business information? Or will having another hard drive eliminate that?

I'm running a couple different programs for viruses and such.

Should I just bight the bullet and upgrade with a new computer as I did with my software?

Thanks in advance!