You'll recall the Rev. Angela Mather and her cash-strapped parish in Lower Walnut, Maine: a use case for free and open source software and other solutions for congregations.
One of the problems she had was an old Windows computer that was sluggish and temperamental. A friend from seminary thought it might be infected with viruses.
But anti-virus programs cost money or lead you on with a limited version. But there is a free (intellectually and financially) version called ClamWin that she can use. There's also a portable version you can keep on a USB drive in case you have to use a strange computer.