Yet Another Cycling Forum

General Category => The Knowledge => Ctrl-Alt-Del => Topic started by: slope on 11 June, 2020, 06:03:33 pm

Title: Has my iMac been hacked? UPDATE
Post by: slope on 11 June, 2020, 06:03:33 pm
2017 iMac, 27"

This screen appeared after a ~15 minute period of un-use whilst I was on the phone TODAY!

Should I be freaked out?

My desktop is a plain grey colour and NO screen saver is set in System Preferences

(https://live.staticflickr.com/65535/49994972538_c0f0808caf_h.jpg) (https://flic.kr/p/2jaTix9)IMG_2622 (https://flic.kr/p/2jaTix9) by slopeslopeslope (https://www.flickr.com/photos/131101502@N05/), on Flickr
Title: Re: Has my iMac been hacked?
Post by: rusky on 11 June, 2020, 06:16:21 pm
I would say that's a graphics issue on the log in screen
Title: Re: Has my iMac been hacked?
Post by: Kim on 11 June, 2020, 06:21:23 pm
Rule of thumb: When someone suggests a computer might have "been hacked" it nearly always hasn't.  It's an example of the Dunning-Kruger effect.

Is this the model of iMac that was notorious for graphics card issues?
Title: Re: Has my iMac been hacked?
Post by: Cudzoziemiec on 11 June, 2020, 06:23:31 pm
Your iMac has either dropped some acid or is trying to play Loony Toons. The two might be indistinguishable.
Title: Re: Has my iMac been hacked?
Post by: grams on 11 June, 2020, 06:28:58 pm
A few people with similar issues and screenshots if you search “iMac rainbow circles login screen”. Probably hardware.

I’d assume the first thing that happened is it kernel panicked and rebooted itself, hence the login screen.

Quote from: Kim on 11 June, 2020, 06:21:23 pm
Is this the model of iMac that was notorious for graphics card issues?

There are some that aren’t???
Title: Re: Has my iMac been hacked?
Post by: ian on 11 June, 2020, 06:42:43 pm
It's just the usual graphics card mishap, I'd assume it will disappear with a reboot, or if you stop taking ketamine.

Generally, the best way to see if you have been hacked is to see if your computer boots into MovieOS.
Title: Re: Has my iMac been hacked?
Post by: TimC on 12 June, 2020, 02:05:23 am
Quote from: Kim on 11 June, 2020, 06:21:23 pm
Rule of thumb: When someone suggests a computer might have "been hacked" it nearly always hasn't.  It's an example of the Dunning-Kruger effect.

Is this the model of iMac that was notorious for graphics card issues?

That was the 2011 27”. I have one. The general symptom is a forest of random horizontal coloured lines. I doubt you can get the graphics card now, but last time I looked it was about £600. The thing has been boxed up in my garage for 2 years. If you’d like to investigate it, feel free...
Title: Re: Has my iMac been hacked?
Post by: tonycollinet on 12 June, 2020, 06:32:32 am
That is a really weird pattern for a hardware fault.

I've never seen hardware faults creating circular patterns. Due to the nature of graphics hardware, faults usually result in horizontal, and/or vertical artifcats. Such a fault would also be unlikely to neatly display the user icon untouched in the centre.

Unless there is somthing specific to advanced graphics engines that can do this. If so, I'm sure Kim will be along in a moment to correct  me. :D
Title: Re: Has my iMac been hacked?
Post by: grams on 12 June, 2020, 09:15:24 am
The circles are because the login screen has a subtle gradient and a corrupt lookup table is mapping each shade to random colours.

I suppose it could equally be software at fault.
Title: Re: Has my iMac been hacked?
Post by: slope on 12 June, 2020, 09:24:13 am
Thank you for all the responses  :thumbsup:

My embarrassing ineptitude at internet "searching" failed to deliver grams' suggestion.

Yes, it does disappear when touching anything on the keyboard.

It appears occasionally and randomly when the computer is in sleep mode. I woke up the other morning to to be greeted by it!
Title: Re: Has my iMac been hacked?
Post by: ian on 12 June, 2020, 09:31:45 am
Do the usual PRAM and system controller resets and perhaps try starting up in safe mode (hold shift when it boots) and see if it continues to happen.
Title: Re: Has my iMac been hacked?
Post by: slope on 12 June, 2020, 10:58:38 am
As with any intermittent issue, it does lead a merry dance ::-)

It's only happened 3 times so far - with days of normality in between times :-\
Title: Re: Has my iMac been hacked?
Post by: Andy64 on 13 June, 2020, 01:51:54 am
I know nothing about Macs etc, but a quick google image search brought up this thread, with a very similar display
https://discussions.apple.com/thread/250170887
Title: Re: Has my iMac been hacked?
Post by: TimC on 13 June, 2020, 08:55:40 am
Interestingly, despite what I said earlier, graphics cards for the 2011 iMac 27" (AMD HD6970) are available at reasonable price - relatively speaking. The same graphics card was used by a number of high-end laptops, and the firmware can be flashed to be compatible with MacOS. Amazon link (https://smile.amazon.co.uk/dp/B086D3KHN6?tag=amz-mkt-fox-uk-21&ascsubtag=1ba00-01000-org00-win10-dsk00-smile-uk000-pcomp-feature-scomp-wm-5&ref=aa_scomp).

Apple replaced the card free of charge on that model for computers up to 4 years old. It may be that they'll do the same for a 2017 model.
Title: Re: Has my iMac been hacked?
Post by: ian on 15 June, 2020, 09:28:36 am
If it's a consistent issue that goes unfixed by the usual things, I'm sure you could persuade them to replace it for a 2017 machine. They swapped out the wifi card in a five-year-ish-old Mac Mini for me.
Title: Re: Has my iMac been hacked?
Post by: slope on 03 July, 2020, 11:32:48 am
Nearly three weeks on after resetting the SMC and PRAM, the problem hasn't returned  :)