Why does my computer get attacked every time I turn it off?

I have webroot plus on both my home desktop computer (connected to internet via ethernet cord which is in turn connected to the wireless router provided by my internet provider) and my laptop (connected to my wifi network which is password protected).   
 
I've never had a virus or threat detected when I scan with webroot manually but everytime i turn back on either my desktop or laptop (after completly shutting down for the night)  the little "threat neutralized" window pops up in the lower right hand but seems to indicate webroot took care of anything that was wrong.    Is there someone/virus acttually attacking my computers every single time I shut down or does turning off and on a computer somehow create a threat as seen by the progam itself?