We used a custom Python script which was specifically programmed for this giveaway. It uses the Twitter Public API to download a list of all @dbrand followers, as well as a list of all @MKBHD followers.
Once the full lists were loaded, the script generated a list of IDs which existed on both lists. This ensured that the potential winner was following both @dbrand and @MKBHD.
From this pool of unique account IDs, random entries were picked using a randomly generated seed based on the NumPy project. These random picks were the resulting winners.
For every subsequent winner selection, the script ran again. This triggered the Twitter Public API follower IDs fetch again. The script downloaded the newest followers and kept going until it reached the followers which were downloaded during the previous run. This saved us from having to download a list of several million followers every time a winner was selected \u2013 while also ensuring that everyone was included and had an equal chance of winning for each random draw.