Update US symbol list & categories function does NOT use Yahoo as a source. It uses official Nasdaq and NYSE sites.
If you searched the forum prior to posting you would find this: Tools \ Update US symbol list and categories and this: List of US stocks with sector information
Since apparently some people missed that - It should be well noted that this function covers COMPANIES only, i.e. common stocks of companies, those which are listed on official Nasdaq page as mentioned in other thread
Exchange Traded Funds, or ETFs are not on that page. So there is no "error", these items simply are NOT there.
Also note that Update US symbol list and categories WIPES category structure and creates FRESH NEW one.
So all your existing assignments are wiped and new ones are created. That is OK if you only use symbols managed completely by Update US symbols and categories.
You are getting A WARNING that is prominently displayed that says it will make permanent changes
so don't be surprised that changes are done.
It is documented in the manual here http://www.amibroker.com/guide/h_categories.html and https://www.amibroker.com/guide/d_ascii.html
Let me quote the manual:
One-click "Update US symbol list and categories"
Automatic setup and update of US stock database is available from Tools->Update US symbol list and categories menu. This is implemented using new #import command and new ASCII importer commands described above.
The command downloads symbol, sector and industry list from amibroker.com web site and create or update current database with stocks listed on NYSE, Nasdaq and AMEX. It also creates sector and industry structure and assigns stocks to proper industries.
CAVEAT: Be aware that using this tool will WIPE (delete) any existing sectors/industries and replace them with the ones imported automatically.
Any symbol that is NOT part of the update list would have its category wiped too because all categories are wiped. As new ones are created in place you will end up with some random category for symbols that are NOT on the update list.
To keep categories untouched you may open
Formats\symbolandsec.format file with notepad. You would see two last lines like this:
You may experiment and remove those two lines so sector structure is kept unchanged, but this will prevent function from removing/renaming old unused sectors and it may prevent from adding new if you run out of free industry slots. If you don't clean exisiting category structure you will end up with new one added to existing one and if your old structure was invalid/wrong it will stay. Cleaning structure allows to remove old wrong entries, but you are free NOT to clean. Do at your own risk. It may not work. You have been warned.