Simply.. Evolution !!
I did a clean reinstall
Then installed avira free and updated it
then i updated windows 7 to latest updates
Now after 5-6 days of smooth work i m suffering the same problem again
Explore your processes !
I would recommend you to try emisoft antimalware ( free mode ) - ya free
And do a complete scan for more ...... !
REMEMBER : having Antivirus alone won't keep malware away
Some nasty malware needs to be manually treated nastily !
And you can explore your processes and active connections with Hijack free ( comes with that itself )
Check For some unusual activity / process / MAINLY active connections