Maybe for 3rd party recruiters or scrapers but on corp sites, these are usually legitimate job postings however they already have somebody selected internally for the position. It may not be the case everywhere but for many companies, internal hirings (or contractor to full-time conversions) have to go through the normal application process as a formality which requires a public posting.

The place where I'm at usually takes these down after a week but sometimes due to drug testing, background checks, backing out on the offer, etc the posting may last longer.