Microsoft Security Essentials is still our favourite antivirus tool, but its update method can cause some problems. Here's how to change the update interval with a registry hack.
If you keep your computer on all day, MSE should update just fine once every 24 hours, which is certainly enough for the average user. However, if you're using it on a laptop, you might miss out on updates because you're constantly sleeping, resuming or not connected to Wi-Fi at any given time. If you find that you have to constantly update manually to get the latest virus definitions, you may be better off tweaking this registry key to make it check for updates more often, thus increasing the chances it checks while it's on and connected to the internet.
Open up the Registry Editor in Windows and head to HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Microsoft Antimalware/Signature Updates. Right click on Signature Updates, hit Permissions, then hit Advanced. Head to the Owner tab, click on the Administrators group and hit OK. Then, back at the Permissions window, check the box labelled "Full Control" while the Administrator's group is selected.
Next, double click on the SignatureUpdateInterval key, and change the number from something between 1 and 24. This will be the number of hours it waits to check for a new update (the default being 24). Once you've done so, you can change the permissions back (where SYSTEM owns the key and Administrators do not have full control). If all goes well, you should notice MSE is a bit better about staying updated from now on. Thanks Frank!