In your wordpress website source, you can notice that there is a meta tag called "generator" which tells which wordpress version you are using. This causes a serious issue to wordpress sites as they give more information about the WordPress used.
This will be used by hackers, and they can hack your site knowing your wordpress version. Some wordpress verions had severe security bugs which are corrected now. So using a old version is a serious issue.
So these it is safe to hide the wordpress version. This can be done easily. Just add the following code your functions.php file of your theme.
If you feel bad to edit your theme files, then you can use some plugins for doing this. Some are,
During installation ….
Another simple thing which people fail to do is removing their readme.html file, which comes along with the wordpress install package. This file also has the WordPress version. You can see it here, http://example.com/readme.html