As I noted last week, Microsoft has released version 2.0 of its free Microsoft Security Essentials software. Most of the changes are relatively small, but I just noticed one setting that takes care of a longstanding issue.
Several readers have complained about MSE 1.0 hogging CPU resources during its scheduled scans. In version 2.0, you can tame the program with this new setting, on the Scheduled Scan tab of the Settings dialog box:
That drop-down menu allow you to choose a value between 10% and 100%, in increments of 10%. Clear the checkbox if you want scans to complete as quickly as possible and you aren’t bothered by CPU usage.
Other noticeable changes in the MSE user interface allow you to specify that you want quarantined items to be deleted automatically after a specified period of time. This option (found on the Advanced tab) is off by default. If you enable it, the default setting is 1 month.
In addition, you’ll find two new options on the Real-time Protection tab. Enable Behavior Monitoring and Enable Network Inspection System are both on by default. In addition, the option to monitor file and program activity on your computer now allows you to scan only incoming or outgoing files (the default is Monitor All Files).
Ed Bott 
I wonder why this is only “during scan”? This would seem the least important when you consider that most times people aren’t even at their PCs at 2AM. Why wouldn’t you want it limiting its CPU usage any time the PC is being used, especially during noticeable areas like when it’s updating signatures?
Rick, I have no idea why the MSE te4am made his design decision, but I can see the logic. Updates are set by default to come down during normal update periods (typically at 3AM), and on my PC the entire updating process typically about 60 seconds. By contrast, a scan can take 10 minutes to 2 hours, depending on settings.
Well, the biggest improvement for me is that it’s not longer pegging a CPU core for doing absolutely nothing. And I do mean nothing. It wasn’t hitting the hard drive, it was just full steam ahead. I noticed this was happening when it first came out, switched to and then got tired of AVG, came back and it was reasonable until lately. I’ve got four cores, so it’s not too big of a deal (although it probably cut down on my @Home work…), but it was annoying. I haven’t noticed a bobble since. My inplace upgrade failed, it uninstalled the old MSE, forced me to reboot, and then start the upgrade procedure again manually. I’m blissfully a happy customer.
Makes perfect sense to me. My scans happen while I use my laptop, and I turn if of at night. Ive been annoyed numerous times by my pc suddenly lagging, and nothing showing up in the task manager until I chose to show all processes.
Ed,
You really provide a great service for PC users. Thanks so much.
In MSE 1.0 the CPU limit was 50% by default
Good post Ed. There have been some subtle changes with MSE 2 and I don’t have any problem with the default settings and I certainly haven’t experienced any slow down with the computer when running a scan. This is a solid product that requires minimal user intervention\maintenance.
In my experience, limiting CPU Usage for the virus software just makes it run longer, thus being more of a nuisance. Wouldn’t it be better just to make virus scans happen after hours, or when convenient for you rather than making it run at half speed?
James, it is now your choice. Give the CPU free rein for fastest results, or dial back CPU usage for least interruption while you’re working.