Perhaps I'm jumping to conclusions, but does sound like a junk file ... despite cancelling from download window continues to download each time LW is opened. 'IF' it is the same, only answer is to (a) cancel from download window, & then (b) close LW, (c) delete the incomplete folder itself.

'If' it is the same file in question you are dealing with & I have myself, not sure if it affects files around it, but could remove the other decent incomplete files from the incomplete folder before deleting it. After deleting the incomplete folder, create a new one of same name, then return the other incomplete files inside.

I presume you've seen this Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see). This does not list every single virus or junk file, but does list the most commonly found ones to be aware of.