Personally I use the Microsoft security suite and it seems to do the job for me, it is free and compatible with Windows.  

We got the ransom attack on our accounting computer about 2 years ago.  Our accounting girl got suckered (it is so easy to get suckered).  They asked us for $1200 which is a bargain compared to some.   I was able to ignore their demands for $'s because......

We back up weekly.  So I was able to delete the corrupted data files and restore the backups.   It really is that simple.  If you keep you back ups up to date you cannot be hurt in that way.   It is best not keep customers CC# on any online computer....so if you must keep records of sensitive data consider a computer that is offline, and of course back it up in case of media failure.

Large businesses have more volume and therefore more people involved in data storage but for small business these tips may help.