I use Kapersky on my computer at work. I had a load of personal emails - some from friends who have died - going back to 2001. I ran a scan of my email folder and it told me there was a trojan in one very old email. I told it to deal with it and it deleted my whole inbox with no way of getting any of it back.
I even tried posting on the Kerpersky forum. I did get a reply which suggested it could be undone but it didn't work.
There is software to undelete files, however it must be run before the place where the files reside get overwritten by something else.
Delete on a computer usually just removes a reference to the file in the hard disk's "index" of files so that it only appears to have been removed from your computer. Because the hard disk's index says the space the file occupies is empty then it gets overwritten at some point when it's needed. Very often, this probably won't happen until you're fairly low on free space.