Security Updates on days when Windows pc is not turned on

There are days when I don't turn on the Windows 11 pc and so security updates for Microsoft Defender Antivirus are not downloaded/installed on those days. Then when I turn the pc on and check Windows Update, there will be a security update for that day which will install. What happened to the security definitions for those days when the computer was off? Are they lost because the pc was not available? When I go into WU > Update History > Definition Updates I can see the gaps when the computer was off.

The updates are cumulative - they contain the previous updates.

Maybe this will clear it up a bit:

"When updates are published, some logic is applied to minimize the size of the update. In most cases, only the differences between the latest update and the update that is currently installed (the set of differences is referred to as the delta) on the device is downloaded and applied. However, the size of the delta depends on two main factors:

• The age of the last update on the device; and
• The source used to download and apply updates.

The older the updates on an endpoint, the larger the download is. However, you must also consider download frequency as well. A more frequent update schedule can result in more network usage, whereas a less-frequent schedule can result in larger file sizes per download." [Microsoft]

In theory, you get what you need.

Is it also the case that Windows Defender updates to the Engine and Platform, which I believe are monthly, are done via Windows Update or can they be installed, when released, by opening Windows Security/Virus Protection and manually checking for updates? I had a few issues with Definitions not being installed if checking via WU, so I manually check for them on Windows Security. Would the updates to the Engine and Platform be installed if I manually checked in Windows Security? Thanks

For further reading, and info quoted in post 3, go here.

Thanks. I'll check when the next Engine and Platform updates are released and try installing them through Windows Security/Virus & Threat Prot/ Manually Check For Updates before Windows Update.

I'm going to assume then that the next cumulative update bundles and installs all the security definitions issued since the previous cumulative and that should take care of any that I might miss daily if the pc is not turned on. I'm basing this on MS comment about security updates as well as fixes, etc., being included in a cumulative.

Still open for responses to @Mitch question ......

Ok..... @Mitch...... see you have a response.... maybe you can come back here and let us know what you find in history when the opportunity presents.

mackie said:

I'm going to assume then that the next cumulative update bundles and installs all the security definitions issued since the previous cumulative and that should take care of any that I might miss daily if the pc is not turned on.

Click to expand...

Correct. The cumulative will add what's missing but won't overwrite anything that's there already.

Wisewiz said:

Correct. The cumulative will add what's missing but won't overwrite anything that's there already.

Click to expand...

Got it.......... and thank you!

Also... I guess one could say that my pc is vulnerable to those missing definitions until the next cumulative is installed.

Hi @mackie . I've only started using Defender since the clean install a couple of weeks ago. I had problems installing Defender updates which appeared when checking WU. I used Norton 360 but couldn't manually install these updates as Norton takes over and blocks access to Defender. I have no update history since the clean install but the next engine and platform update is probably due in the next week. Will see what happens.

Mitch said:

Hi @mackie . I've only started using Defender since the clean install a couple of weeks ago. I had problems installing Defender updates which appeared when checking WU. I used Norton 360 but couldn't manually install these updates as Norton takes over and blocks access to Defender. I have no update history since the clean install but the next engine and platform update is probably due in the next week. Will see what happens.

Click to expand...

I've been using MS security since Windows 7 and have not had security problems. I think the last time I used another security software was during the Vista days. Did you uninstall Norton before or after the clean Windows install and start of Defender?

Hi @mackie . I tried a repair install first with Norton in place bur the Defender definitions still didn't install. I then uninstalled Norton and Reflect (to remove the licence) and did a clean install. I didn't reinstall Norton (on this PC) although Norton is on 2 others. If you use Norton, you have no access to Defender settings and manual updates unless you uninstall Norton. This desktop PC is different from the other 2. If I run WU check it will download definition updates which appear in Update History- in the other 2, no definitions are downloaded and don't appear in Reliability Monitor which shows installations. No one, seems to know why this is as all 3 PCs were setup the same way. Regards.

I saw where you recently opened a post on this problem, so for continuity purpose I'm going to quote your reply there.