Stalking is a common trait of the sociopath, as they need to have complete control over their partner. I do not recall any time in the relationship when he did not try to stalk me, and track me online. Some of this was based upon paranoia, most of it was based upon the need to control me and isolate me (by accusing me of having affairs with people etc).
Life became complicated, as I had to change all of my passwords. Close down my social networking sites, or at least deactivate. I changed passwords so many times, that i would forget what password I was using.
Often you will only know that you are being stalked when either you are unable to get into your email or social networking as they have changed the password, or more often, when a string of obscenities is yelled at you, for what they have read and taken out of context, with no conscience at all, that they had hacked into your private information. That they have violated you once again, in their mind this is fine and acceptable.
This is the address for the PDF file Digital stalking a guide to technology risks for victims (scroll to the bottom of the page for PDF download)