First, Ransomware. This is a form of malware that looks for data files (Office documents, pictures, that sort of thing) and encrypts them. It then tells you that it will decrypt them for you if you pay them the low, low price of $59.99 (or whatever).
Nice pictures of the kids you have there. Be a shame if anything happened to it.
Like I said, nasty. Enough people pay the ransom that there's an active development in these tools:
So what do you do to protect yourself? You should have an antivirus installed on your Windows (and increasingly Macintosh) computer, but most antivirus is pretty bad at picking up newly released malware. Basically, you're hoping that someone else will get hit before you do, and the antivirus will get updated to detect the new nasty before it discovers your PC.
More importantly, you should be backing up your data. This way, if the ransomware hits you, you at least still have copies of the kid's pictures. USB hard drives are cheap, so there's no reason not to do this every day (or at least every week). Here's a 1 TB drive that retails for $59. At that price, you can get two - as with concealed carry pistols, the rule for backups is "Two is one and one is none".
ASM826 does this sort of thing for a living - he may chime in here with his thoughts. Or not. ;-)