A question for a programmer - I'm not one.

A websites was developed using .NET. The site has data stored in a database
and the users can pull up lists (one at a time) with about a hundred items
in each of them and they can then select items, one at a time, click a
button and it moves them into a new blank list which they can then save.

The current way is too slow for the users as they could need to select 50
items from a list and only being able to move one item at a time to the new
list just takes too long.

The site needs to be modified so that the users can select more than one
item at a time using shift and click and ctrl and click so that they could
select all the items they need in one go from the list, click the button and
move them to the new list.

I've been told that this will be difficult to do. Is this right?