Lots getting past AVG realtime protection it seems?

Hello Theo,
We regret for the inconvenience caused.
Could you please let us know the name of the AVG product you have installed in your pc? also provide us the screenshot of the issue to assist you better. If AVG detects the thread we request you to remove it.
Feel free to contact us for any further assistance. Thank you.

1) Despite running with "Realtime Protection", on running the AVG scan function it consistently finds Trojans and other nasties. Just scanned 9 incremental backups on ext drive and every one infected.

2) Persistent nuisance which might be related - an unsolicited large rectangular popup on screen which won't go away and I can't locate its origin. Invites me to enter my name and password - hah! Says "To view this page you must log in to this area on demo.bw-fla.uni-freiburg.de:80:"  There's a ittle white-on-black square graphic in top left corner depicting at-sign, quaver notes, cloud symbol, and clock symbol. 

Help please!

Hello Aravind, thanks for your response.
Here is - i hope - the information you requested

"name of the AVG product you have installed in your pc?"
Please note - My machine is a MacBook Air, not a PC
AVG AntiVirus
Version 2015.0 (4818)
Virus databases: 12416
Scan engine: 4604
Last update: June 14, 2016
Copyright (C) 1991-2015 AVG Technologies, Inc.   All rights reserved.
" also provide us the screenshot of the issue to assist you better."
Here is a screenshot showing the unsolicited popup. Sometimes it doesn't appear e.g. on a new browser window.
Screenshot of AVG screen with unsolicited popup. Also displaying active programs.

"If AVG detects the thread we request you to remove it."

THeo, For your info, just in case that you are unaware, you can post the screenshot (http://avgclick.me/getscreenshot) here in your topic. Click on 'Answer' & then click on the 'Image' [mountain symbol] & follow the instructions. 
AVG Guru

Hello Aravind, thanks for your response.
Here is - i hope - the information you requested

"name of the AVG product you have installed in your pc?"
Please note - My machine is a MacBook Air, not a PC
AVG AntiVirus
Version 2015.0 (4818)
Virus databases: 12416
Scan engine: 4604
Last update: June 14, 2016
Copyright (C) 1991-2015 AVG Technologies, Inc.   All rights reserved.
" also provide us the screenshot of the issue to assist you better."
Here is a screenshot showing the unsolicited popup. Sometimes it doesn't appear e.g. on a new browser window.
Screenshot of AVG screen with unsolicited popup. Also displaying active programs.

"If AVG detects the thread we request you to remove it."

Thank you Balasubramanian,

I will follow the procedure you outline above - I have other pressing committments, however, so it may be a few days before I can do that. 

There was a slight glitch in my message above - as soon as I had added the image, I found I was unable to complete or modify the message (a bug!). You may notice that it ends abruptly with a quote from your earlier -
"If AVG detects the thread we request you to remove it."
I had intended to add that I'm not sure what the meaning of the quoted text is, specifically "detects the thread" and "remove it".  If this is important I'd appreciate some illumination.
Regards, TB

Hello Theo,

Thank you for providing the detailed information and the screenshot.
We request you to completely reinstall AVG antivirus on your Mac once and then check whether the issue persists.
To uninstall AVG antivirus on Mac, please follow the instructions mentioned in this link: http://avgread.me/1LhhXRT
To download and install AVG antivirus on Mac, please follow the instructions mentioned in this link: http://avgread.me/1ggvK09 .
Please feel free to contact us if you need any assistance.