Yes, you can certainly continue using MT4 and MT5 trading platforms on the unsupported and outdated operational systems after October 2017, only if you have already installed the trading platforms before the 1st of October.

The end of technical support of MT4 and MT5 on Windows XP, 2003 or Vista will disable the following functions.

1. Receiving updates of the trading platforms(both MT4 and MT5).
2. Installing trading platforms(both MT4 and MT5) on these operating systems.

MetaQuotes won’t take a responsibility of any malfunctions or errors while using MT4 or MT5 trading platforms on outdated and unsupported operational systems.

You can still continue running the platforms on outdated OS, but you are recommended to update your device accordingly.

For more information about the “End of technical support”, please refer to the article here.