Link>
Welcome!Unfortunately this router has entered in to EOL status I believe and will no longer have any development done one it. I'm not sure why, however, this router never saw any FW updates over the years since it came out. I actually never have even seen one of these in person.
I recommend if the router is working, keep it going. If not, then upgrade to a more newer generation model router. If your looking for this same class router, I believe the DIR-835 has the same specs as the 665. Also the DIR-857/DIR-836L is as well. The 835 and 857 are still live however not sure for how much longer. There hasn't been any FW updates and from what I know, unless it's a major security flaw, there won't be any thing forth coming. I have the 835 and 857 routers and they are very stable and work very well.
The 665 seem to be a one off router for some reason that didn't seem to follow D-Links model vs spec marketing. We see that most 5 and 6 series models are all single 2.4Ghz band routers, while DIR 8 series are dual 2.4Ghz and 5Ghz band routers. This 665 didn't follow that for some reason. It's an odd ball for sure.
Sorry that I can't be of more help.