“new” post indication in category widget

Hello everybody
I have a couple of categories and some posts added in them. I’ve set “Categories” widget to be displayed on the right side that shows Categories with post count, like this:

Prisoners of War (34)
The Truth (86)
Katyn Documents (122)

Now what I want is that whenever a new post is added in a category, it should show some indication in front of category name, so that user may be able to know that the category contains a new post, like this:

Prisoners of War (34)
The Truth (87) “new”
Katyn Documents (122)

The “new” in front of “The Truth” means a new post has been added in PHP category. It is not necessary to show the text “new”, we can have any type of indication like link color is changed, bold font or anything else.
I hope you’ve understood my point. Please help me in this regard. I don’t care if there is a ready-made widget available for this or I have to modify code of category widget