Check out this forum:
https://forum.avast.com/index.php?topic=174033.0
Nearly from one week, i found my system also running slow. I take it lightly. With passage of time, it goes slower and slower. Then i came to know its infected with virus. Even, it takes control over my browser and it behaves abnormal. Whenever i am trying to search any query, it redirect me to some unknown site.
After that i decided to remove it from my system. Now its working well.
For more detail visit this link - howtouninstallamalware.com/how-to-uninstall-pup-datingsmith-malwarevirus-and-adware-windows-xp7810