i have been having this problem also and i have a hacker, so you may want to make sure all your malware software is working correctly because they can disable anti virus and malware software. i have been thru 5 anti virus and the hacker dismembered all
of them. this may not be your problem but malware is very well hidden and if you see something strange always check it out. i found out the hard way but now i know what to look for. problem is i cant find anyone that can get it out of my system.
once again may not be the problem but thought i would add this to the replies.
if you want anymore info let me know, i have taught myself how to deal with the hacker just cant get rid of him and yes its a him. Got his IP address and found him...in CHINA!
cjyp