Generally when typing, the cursor appears after a letter. But in rare cases, sometimes the cursor highlights the words instead. This is a common issue with anyone who types regularly using a text editor or word processor.
The first time this happened with me, I had no clue how it happened and It took me a while to figure out how to switch to the normal cursor highlighter. It did cause me a little bit of frustration, but everything was sorted in the end.
A few searches on the internet, and I came to know about the exact cause of the problem. This is actually an alternate typing mode in windows which can be enabled by pressing the INSERT key.
How to disable cursor highlighting letters while typing
If you accidentally pressed the INSERT key while typing, windows would switch to an alternate overwrite mode. This can be reverted back by pressing the INSERT key once again.
Most modern text editors allow users to choose from two modes. Namely insert and overwrite mode. Insert mode is enabled by default. In this mode the letter is inserted where the cursor is positioned. Alternatively, in overwrite mode, the letter is replaced on the highlighted character.
This is one of the less known things about text editors and now that you know about it, you can easily switch between the both as and when you require.