This update only applies to Win 7 - there was no analogous patch released for Vista.
If you are a Win 7 user, please see Woody Leonhard's Info World article Microsoft releases KB3161647, KB3161608 to fix slow Windows 7 update scans for details on the latest patch for the Win 7 Windows Update Agent.
Updating drivers is also a great troubleshooting step when the device is having some kind of problem or is generating an error, like a Device Manager error code.
I did not encounter this problem with MSN version 8.0.
Here are the details of the affected SW version: The MSN build number is v8.1.0178.00 or later.
As Sea Monster noted, if you leave Windows Update running for several hours and don't see an error message you might find that "Checking for updates..." will eventually run to completion and allow you to download available updates.
If that doesn't help, please see the step-by-step instructions I posted on 16-Jun-2016 in m#l's thread Updates not working, it has been searching for updates for hours in the Microsoft Answers forum for a possible workaround.
It's one of the best sources of information I've found to date on these slow Windows Updates and any new developments will likely be posted there.
----------- System Manufacturer/Model Number HP Pavilion dv6835ca OS Vista Home Premium 32-bit SP2 CPU Intel Core2Duo T5550 @ 1.83 GHz Motherboard Quanta 30D2 (U2E1) Memory 3 GB RAM Graphics Card NVIDIA Ge Force 8400M GS Sound Card Realtek High Definition Audio System Manufacturer/Model Number Custom Built OS Windows 7 Professional x64 Windows Vista Business x64 CPU Intel Core i5-3570 @ 3.4GHz Motherboard Asus P8P67 Pro Memory 12GB DDR3-1600 Graphics Card NVIDIA Ge Force GTX960 4GB Sound Card Realtek HD Audio (Built in) Monitor(s) Displays Dell E2210H, Dell E2010HC Screen Resolution 1920x1080, 1600x900 Keyboard Dell Quietkey (Once again old, but feels great!
This temporary workaround was also suggested in Scousa JAY's thread, but that thread was started in August 2015 and currently has over 200 posts so new visitors might have a problem finding relevant information.
I'd still advise you subscribe to Scousa JAY's thread hread windows update just seems to hang while checking and read through some of the recent posts by other users, though.
The current Windows Update Agent v7.6.7600.256 for Vista at C:\Windows\system32\has not been updated by Microsoft since June 2012.