Taking those in reverse order:-

do a restore to the week before last sometime as I haven't changed anything that I can remember. I could then do a manual definitions update which should not contain the buggy ones.

I don't like this one bit. Presumably the problem update contained something useful as well as the bug, and if so you will lose that. I wouldn't even be certain it would work;

the fix involves Safe Mode to get onto the web, then running a file which will allegedly fix it all ... I'm just wary about running yet more McAfee script on my computer.

Messy. A toss-up between that and TechGuyUK's recommendation I would say, though I would be tempted to try his way first. Note it needs to be Safe Mode with Networking, not pure Safe Mode, if you go that way.

My recommendation, because I'm so strongly against the product, would be to download the McAfee delete routine, (like some or all Norton products you can't just delete it properly - in fact IIRC it can re-install itself), and choose one from the AV Comparatives list instead. A few quid wasted by losing the outstanding McAfee subscription could be worth it for peace of mind. Particularly if you pick one of the free ones. The last time I looked most of those have higher detail scores than McAfee.

If you turn on Windows Firewall and run in Safe Mode with Networking to do this, you should be fine. Watch out when installing new ones though, that the McAfee Firewall is definitely not running. Many products can stop competing ones installing. Windows Firewall is usually OK and allows them.

In reply to a post by GeoffB:

...Can anyone say which would be the better solution. I'm just wary about running yet more McAfee script on my computer.

http://service.mcafee.com/FAQDocument.aspx?id=TS101331 - I used it successfully a few years ago for a thorough mcafee clean out before installing another AV program because any bits and pieces left behind by mcafee can cause a corrupt or failed installation of other AV software�

Also just to note, as usual, use the built-in Add/Remove program uninstall method first, ideally in normal Windows (not safe mode), and then follow up with the removal tools second. The norton removal tool is a partial exception as sometimes it invokes the native uninstaller as part of the process.

Can not remember whether mcafee has it's own uninstaller but the document I linked to suggests using Windows Add or Remove Programs/Programs and Features for the uninstall and as you say must be done in normal Windows.

In reply to a post by 4M2:

Can not remember whether mcafee has it's own uninstaller but the document I linked to suggests using Windows Add or Remove Programs/Programs and Features for the uninstall and as you say must be done in normal Windows.

That document links to the MCPR (McAfee Consumer Product Removal Tool) but states to use add/remove first (or Programs & Features as its known in Vista, Win7 and Win8).

Interestingly I was called to a Dell Inspiron desktop today that could not connect to the Internet since last Saturday (18th). I could not ping the router, but the card was taking DHCP info from the router. Checked the router with a laptop and it was fine. Thinking there was a network card problem I re-installed the driver, no change. Then inserted another network card and installed it ok. It too took DHCP info (ip address etc) but could not ping the router. Tried a USB wifi dongle which also installed ok, but could not connect. Examined event logs and the Mcafee logs but only confusing information seen. Having read this thread and visiting the Mcafee site I am suspecting this AV software (not the first time Mcafee have done this, a few years ago one of their updates devastated every computer in the school where I worked.) Once I get permission from the owner I think I'm going to send this product to the great big gashbin in the sky.

In reply to a post by jchamier:

In reply to a post by 4M2:

Can not remember whether mcafee has it's own uninstaller but the document I linked to suggests using Windows Add or Remove Programs/Programs and Features for the uninstall and as you say must be done in normal Windows.

That document links to the MCPR (McAfee Consumer Product Removal Tool) but states to use add/remove first (or Programs & Features as its known in Vista, Win7 and Win8).

Sure

What I've just noticed also is that the removal tool has become bloated also: I've still got the one from 2009, version 2.0.155.1, which is less than 600KB; now the tool is more than 2MB.

In reply to a post by mandrake127:

...(not the first time Mcafee have done this, a few years ago one of their updates devastated every computer in the school where I worked.)...

And my LAN - amongst other things it became impossible to "see" other devices on the network and obviously file transfers were impossible. So I battled with it for a few days, after that terrible update a few years back, got nowhere with it and trashed it!

Further to the above the owner is very reluctant to lose the Mcafee software as he has just renewed his installation fee. Examination of the Mcafee logs does suggest an update occurred after which this problem was encountered. Fortunately there was a restore point from the day before. Restored to this and was able to re-acqure the internet connection. Downloaded and ran the Mcafee Virtual Tech as recommended on their TS101446 and it has found 5 problems, including two registry key fixes and a core fix.
On your laptop examine the Mcafee logs and try and determine if an update occurred at the same time as your problem. A handy restore point would be nice. Alternatively Mcafee's Safe Mode with networking workaround might be doable. Here the desktop PC now appears good, but the owner has been without the Internet for a week all due to Mcafee. (If I had my way, I would get all the spyware/virus writers in the world and amputate their hands, then shoot all the AV people, but I suspect that would seem over the top. ☺ )

If the owner had any cells left in his brain he would cut his losses and uninstall the McAfee software immediately given the chaos it has caused, and install a free alternative. But no doubt he thinks McAfee is great and has proteted him from thousands of viruses and hacking attempts. The lack of internet for a week and £30 renewal fee being a small price to pay