I hear it a lot. "Help, I got a virus! What should I do?" When I ask what anti-virus program they were using to protect themselves it's often greeted with a sheepish "Well, the program expired and I meant to update it but..." Sound familiar?
Whenever the topic of anti-virus comes up for personal use I suggest people consider Sophos. This well known anti-virus vendor offers their product free for home use, and one account will protect up to 10 computers. It even supports both PC and Mac! That's easily a $250/yr value for free.
No ads, no nag messages, just free protection that you can centrally manage from a web page. You don't need to be a tech guru to run it, and you can protect all your computers as well as your mother's system so she doesn't get infected again. (Sorry mom, but prevention is easier than another panicked phone call.) You can check it out at https://home.sophos.com
I can hear some of you now saying "But I don't need anti-virus, I own a Mac!" Let me stop you right there. Viruses exist for Mac's. It's a fact. Google it. What you need to ask yourself is "Why would I risk a virus and possibly all my data when it costs me nothing to protect it?"
As an added bonus the program will let you control what kind of websites each computer can visit. Want to make sure the kids aren't surfing inappropriate sites on their laptops? Sophos has you covered.
You can assign controls by easy to use categories and let Sophos do it's thing. Below is an example. I strongly recommend using a self-updating anti-virus program as basic protection for your computers, otherwise you're asking for trouble.
There are other free anti-virus programs out there, however this is one of the most robust offers I have seen and the price is certainly right. The interface is easy to manage even with no technical knowledge and the underlying protection is good.