Many people probably already know about this, but I had to deal with it again today so thought I'd post it just in case it might help someone else.
Judging by Google and Youtube, many refrigerators of many different brands have this problem of water leaking into the refrigerator.
When the heater comes on for the automatic defrost of the cooling coils, the melting water runs down and into a drain hole under the coils which takes it to a pan for evaporation. The problem happens if this drain line freezes solid and the melted water has nowhere to drain so it runs down into the refrigerator section, and in severe cases, out onto the floor.
Our fridge is a Kenmore with top freezer (made by Whirlpool) so the first time this happened my wife thought the water line to the icemaker was leaking inside the fridge so she called a Sears serviceman. He knew exactly what the problem was when he arrived from seeing it many times, proceeded to remove the panels inside the freezer to expose the coils and the drain hole, and it was iced over and plugged solid. He used a heat gun and hot water to thaw the line, put the panels back on and charged us over $100 for the "repair".
And of course it happened again, in fact a couple of times, but now that I knew what the problem was I could take care of it myself. But it's aggravating to have this keep happening so I researched online trying to find a way to solve the problem permanently. Found that this is a very common problem and they do sell a kit that is supposed to fix it so I went ahead and ordered one to be ready for the next time I had to take it apart and thaw it out.
So today the drain froze up again. After thawing it this time I added this probe to see if it will solve the problem. It's a very simple fix if it works, just attaches to the defrost heater running below the coils with the probe going down into the drain hole to transfer some heat into it when it defrosts. All reviews I saw were good for it, and saw some comments from people saying they had done the same thing with a piece of copper wire. Time will tell whether or not it works for me.