@ImtiazAli   At first, yes.  However, after typing that, and thinking some more, I completely removed my ISP router, and just have my WAN going right into my XE75.  3 days later, it's been okay, which is the longest in a while.

  @ZMan2k2 i started getting same messages a couple days ago against a wired dumb device that has never been a problem for the past couple years I have had the router and this device.
 

own a deco xe5300 with latest 1.3.2 firmware. It has to be a false positive.

  @MacMaven234 For me, it switched from IoT devices to tablets, phones etc.  So far, my latest setup is working positively.  I swapped my ethernet cord from my ISP modem and the XE75 and put the modem into bridge mode.  So far, since I posted, it's been quiet.  

Well, that went well.  Lasted less than a week.  The indicator in the deco app has gone from tablets, laptops, phones and now my home theatre receiver.  There is no rhyme or reason to the pattern, just frustration.  I'm afraid that I'll miss an ACTUAL warning because I'm about to dismiss ALL OF THEM!   

Okay, here's where things get weird.  
 

Pinterest.  Specifically recipe posts.  The more I post here, the more different things I investigate.  Well, since Thursday I've had 3 such warnings, including today.  I stopped my wife, got her to show me what she was browsing, and now I can replicate it, almost every time.  Is there something that I can do, with TP Link/TrendMicro that can remedy this?

Nope, not Pinterest.  Google chrome, more specifically "Enhanced safe browsing " for chrome.  Put it on "standard " and even Pinterest doesn't set off warnings.  I'll post if anything changes.

Things changed.  I had to remove all my extensions (ie. AdBlocker), and reset Chrome to its original settings in the menu.  Close and reopen, and try for a few days, and so-far-so-good.   BTW, if you use Firefox, or in my case "try", it should stop things from setting off alarms as well.

Last post on this.  After working with my ISP, many hours of network configuration, experimentation, etc., I've finally stopped the "Malicious network attack" warning.  I took the Deco OUT of router mode and put them in Access point mode.  The router function was causing WAY TOO MANY errors and glitches, and by turning the Deco into a "dumb" AP, my problems are solved.  
 

Congratulations TP Link, you've made some expensive Apps and rendered your security subscription (which mine was coming up for renewal) useless.  You've ost a client in me.  I can't in good conscience pass the Deco on to anyone else for all the problems, so I've lost a lot of money.  Bravo!!