In the early 2000s and 2010s, numeric filenames were the standard for file-sharing forums and bulletin boards (BBS). These sites used automated scripts to rename uploads to prevent duplicate entries and to obscure the contents from early search engine crawlers. "23708.rar" is a remnant of this era of digital anonymity, where the user had to know exactly what the number corresponded to via a separate index or forum post. Conclusion
Are you writing about conventions?
Malicious code can be hidden several folders deep. 23708.rar