Let us say I have bought a stock XYZ at $100 and I have a stop loss order at $95. Some bad news comes out suddenly, or maybe a flash crash happens, so the price drops from $100 to $90 and trading gets halted. (I guess if a stocks drops 10%, trading will get halted?) Will my stop order still be triggered, considering trading got halted?
During a circuit breaker, no trading occurs.
These policies have been implemented to maintain exchange liquidity since the NYSE nearly went bankrupt during the 1987 crash because many members had become insolvent.
If an order is filled before the halt, it will stand unless busted. During the Flash Crash, many orders were busted.
quantycuenta is right, if a halt is in place, then no trading will occur, simple as that. But in the practice of risk management it is a little different.
Want to remind you that you are assuming that trading is halted immediately upon the drop in price. That doesn't always happen, so if there is any time between the actual price drop and halt of trading, then it is possible that your order will be filled, depending on how liquid your security is. Also not every security has circuit breakers in place and the exact requirements to trigger a breaker is not public information.
In some cases, trades are ordered to be rolled back (reversed) by the exchange but this is usually reserved for institutional traders who make some sort of mistake.
This article below mentions day traders who bought at or near the bottom of the May 6, 2010 flash crash. This was before circuit breakers but I think it's a good story for someone looking to understand the finer workings of the electronic market.