Norton Security was recently ( a week or two ago) automatically installed on my computer without my permission when I was away from the keyboard by a program called "Norton Security Scan" that I've had for a long time.

For about three days now, several times a day files of the following pattern (long number varies)
C:\Windows\Temp\opera autoupdate\opera_installer_20168174929173.dll
and
C:\Windows\Temp\opera_installer_20168171540162.dll
are being blocked and quarantined, having been categorized by Norton as Heur.AdvML.B

There are also some in a different folder - such as c:windows\syswow64\config\systemprofile\downloads\opera autoupdate\opera_installer_201681736254774.dll

It is the ones in the main Temp folder that are getting Quarantined, and these are for Opera Beta, so I suspect the ones in the opera autoupdate subfolders may be for Opera Stable. These are getting blocked rather than Quarantined.

I did a Live Chat but I felt uneasy about giving remote access to my computer to someone whose name suggested there was a high chance that he was in a third world country (India). He suggested I also use Norton Power Eraser but that didn't find anything to do with Opera.

Both Opera Stable and Opera Next are saying that they are up to date, so it is questionable whether Norton Security is actually succeeding in blocking updates, though the opera_autoupdate.log in the C:\Windows\Temp\opera autoupdate\ folder says
[3092:3948:0817/173636:333935:WARNING:ipc_channel_win.cc(371)] Unable to create pipe "\.\pipe\chrome.oauc_task_pipee59e7323ed1cebd78082538c8b9cbe70" in client mode: The system cannot find the file specified. (0x2)

The one in the c:windows\syswow64\config\systemprofile\downloads\opera autoupdate\ says
[3744:6912:0817/172409:29640876:ERROR:ipc_channel_win.cc(213)] pipe error: 109

The one in the main C:\Windows\Temp\ folder says:
[3092:3948:0817/173636:333935:WARNING:ipc_channel_win.cc(371)] Unable to create pipe "\.\pipe\chrome.oauc_task_pipee59e7323ed1cebd78082538c8b9cbe70" in client mode: The system cannot find the file specified. (0x2)

Control Panel\Programs\Programs and Features only shows two versions of Opera on my system:
Opera beta 40.0.2308.11
Opera Stable 39.0.2256.48

Probably Opera Turbo has turned itself on? Check the pull down menu on the left and if you find a way of turning Turbo off FOREVER pleeeeease tell me!

I have never used Opera 12 - I started in Opera at version 15, having previously used mainly Firefox - which I still use for some purposes.

Here is what is wrong with all Opera 15+ (Chromium) versions

1. Too few settings are available for changing things
2. No Print Preview, which means you can't get a page to print how you want it - as a result I always access certain sites through Firefox because I have work-related things I need to print from them
3. Alt-D does various things, doesn't always take you to the address bar so you can start typing a URL. I use my browsers fast and I don't want to have to think about where I am before I press Alt-D
4. Opera Turbo comes on without warning, and as far as I know cannot be blocked from doing so; the result being that I find I can't access web pages, and then after a while, sometimes a long while, having tried Firefox, I suddenly think "I wonder if Turbo is on"
5. In the very latest versions I keep getting a pull down Opera menu appearing in front of other applications after I have used Alt-Tab
6. Lack of a Bugzilla style interactive community bug reporting system - as a result there is no way of knowing whether Opera is listening to your concerns

I found I had somehow been put into "Off-Road mode" (in the main menu found by clicking the top left button). Thank you leocg.