Where the name comes from
In Chromium's source code, a download marked as dangerous gets a temporary name: the word Unconfirmed, a space, a random number and .crdownload. Chrome in another language translates the first word: Sin confirmar in Spanish, Nicht bestätigt in German, 未確認 in Japanese.
The real name is kept aside. The file only takes it once the download is accepted.
Why Chrome flagged it
Google lists the reasons: the file may be malware or software that changes settings without asking; it may be uncommon, or packed to avoid detection, as in a password-protected archive; Safe Browsing may be turned off; or the file may have come over an insecure connection.
What to do
- Open the downloads page (
chrome://downloads) and read the warning on that entry. - If you do not know the site or did not expect the file, delete it. Google asks people to take these warnings seriously: attackers sometimes tell their victims to ignore them.
- If you trust the source and keep the file, Chrome gives it its real name.
If you do nothing
Google says a blocked download leaves the download history after an hour if you take no action. Once Chrome is closed, an Unconfirmed file left in the folder is not in use and can be deleted. To get the file, download it again from the original page.
Nothing to repair
An Unconfirmed file is held back, not damaged. Once you decide on the downloads page, Chrome either gives it its real name or removes it. Crdownload is for the other case: a download that stopped and left a partial file.
Common questions
Is an Unconfirmed .crdownload file a virus?
Not necessarily. The name says Chrome flagged the download, not what is inside. Read the warning and check where the file came from before keeping it.
What does the number mean?
Nothing about the file. Chrome picks a random number for each flagged download, so the name changes from one to the next.
Can I rename it myself?
Deciding from the downloads page is the safer way: the warning is there to read, and Chrome gives the file its real name itself when you keep it.
Sources
Documents consulted for this guide.