TROUBLE WITH MY COMPUTER

I was looking on my computer last week when all of a sudden there came a screen on saying my computer had a virus and it was ready to crush.   I didn't know what to do so I called Staples (the store I bought my computer from a year ago).  They told me not to touch anything and to bring it in.  There was a virus.  I do have Norton Virus protection but the virus got through.   I did have to pay for them to fix it  So $150.00 later my computer is up and running again.  Hopefully it won't happen again.