SKTimeStamp is a simple Explorer extension which makes it easy to change the timestamps of any file.
Why should you care? Normally you probably won't, but occasionally file dates can give away more information than you'd like (you may not want your boss to know that the presentation you've handed in was actually only completed at 3am this morning, for instance). Or if, say, you're distributing a set of files to the public then it will probably just look neater if they all have the same "last modified" date.
Whatever your reasons, once installed SKTimeStamp can update your files dates and times in no time at all. And it does this by adding a new tab to your file properties dialog: just right-click a file in Explorer, select Properties and click Time Stamps to see its Created, Last Modified and Last Accessed times.
Once you're there, simply clicking the "Touch" button will update the "Last Modified" stamp to the current time.
Alternatively, you can manually set any of the times to whatever you want. Even making a file look as though it was created after it was last modified, if you like (though beware, that may not be a good idea, as it may cause programs which make use of these dates to misbehave).
And if you need to change the dates of a group of files simultaneously, just select them all in Explorer before opening Properties, and your SKTimeStamp tweaks will work on the entire batch.