Automatic Hyperlink

New text formatted as a hyperlink (.com and such) is hyperlinked automatically. That works just fine. Here is my problem:

I have a pre-existing Excel document (created by a former coworker) with three worksheets. Each worksheet has a column with about 400 cells containing web addresses and these are not currently hyperlinked. I can manually go to each cell, place the cursor at the end of the text, and hit enter. The text is now a hyperlink. I would rather not do that manually for 1200 entries. Is there an easier way?