Q: iMac late 2013 lost usb connection after efi smc update

Did you try an SMC reset? http://support.apple.com/kb/HT3964

You are not the only one with a new iMac + Mavericks + one or more external USB products. For me it happens when I hook up my iPad or iPhone. Have a look at this topic: https://discussions.apple.com/message/23506859#23506859

having the same issue with my  mac loosing connection to usb and bluetooth  , have to power button restart to get it back

I'm having the same issue with my new 27", 3TB FD iMac which was already shipped with Mavericks.

You are still under warranty, so contact Apple support.

Apple Support Contact

wondering if any one  having this problem  used time machine  to transfer  info from  an older machine  ?

Sorry, but the support was not very helpful in this case. The man on the phone told me to do SMC reset, permission repair and so on. After that he told me to test each USB device I have on every USB port on the iMac and look if the error persists - sorry I want to work with my mac, not to test it.

In the end I think I have the same problem as many iMac-2013-FusionDrive-Mavericks-Users here: USB does not work correctly!

Same problem here. In my case it happens when I connect USB DAC. External USB hardrive works ok.

Any solutons yet or I will have to return the iMac.

Same issues here! Hopefully the 10.9.2 update will fix it.

Exactely the Same issue with my iMac 27-fusionDrive3T late 2013, having USB HDs for time machine and data. I contacted the Apple support who propose first level  of support: resets SMC, hard reset and so one without success . I did several trials removing hubs, using different USB (3.0,2.0 and 1.0) and changing devices connections(direct to iMac or through USB hub). I succeeded to find a stable configuration puting audio USB speaker  directly connected to IMac. When I put this USB speaker through USB huband  launch itune music after a certain time all USB chain freeze, and by consequence no more possibility to control the iMac with keyboard, trackpad .... IMac is still working,!  The only possibility is to reboot the machine with tne reset button. Hope also this will fixe in the future OSX release!

With the OSX release 10.9.2 now is fix for me. No more freeze watch ever the USB configuration. I am now able to use all the USB peripheral as it was the cas with my previous iMac.