Google produced this: https://www.google.com/#hl=en&sugexp=les%3Beaqth&gs_nf=1&gs_mss=microsoft%20security%20essentials%20slow%20s&cp=38&gs_id=1qi&xhr=t&q=microsoft+security+essentials+slow+scan&pf=p&sclient=psy-ab&oq=microsoft+security+essentials+slow+san&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=cd0820781f4eef2e&biw=1280&bih=887
Note that there is often additional details added by other users, might be helpful if this were noted here as well. You have a second antivirus or a trial version installed on your system?
Get WOT (World Of Trust) add-on for your browser if you do not have it. Much safer to visit websites than before. http://www.mywot.com/
Once WOT is installed, you have better choices on what is safe to visit.
How long did the scanning task take?
I recently switched over to Microsoft Security Essentials for my virus scanner. I have it scheduled to scan usually on Sundays, but today, I got an 'alert' when I was visiting a news story from Yahoo. So I started a scan, and went off to do some things. 3 hours later, the scan is still running. I've never seen it run that long. I watched it for a while to see where it was scanning, and noticed it seemed to be scanning in the same place it was when I left 3 hours ago.
It finally switched to my F (recovery) drive, but I'm not sure if there is something going wrong with this program.
Has anyone else run into this problem with this program?