1. A method of managing content site visitor profiles, the method comprising: under control of a hardware processor: receiving first visitor data from a first data collection tag embedded within a first content page, the first visitor data comprising (i) data indicative of user interactions with the first content page, (ii) a cookie-derived visitor identifier associated with a first visitor visiting the first content page, (iii) a first identifier, and (iv) a second identifier different from the first identifier, the first data collection tag comprising instructions to gather the first visitor data and report the first visitor data to the hardware processor; identifying the first identifier and the second identifier from the first visitor data; generating a first combined identifier from the first identifier and the second identifier; adding at least some of the first visitor data to a first visitor profile; receiving second visitor data from a second data collection tag embedded within a second content page, the second visitor data comprising (i) data indicative of user interactions with the second content page, (ii) the cookie-derived visitor identifier, (iii) the first identifier, and (iv) a third identifier different from the second identifier, the second data collection tag comprising instructions to gather the second visitor data and report the second visitor data to the hardware processor; identifying the first identifier and the third identifier from the second visitor data; generating a second combined identifier from the first identifier and the third identifier; determining whether the first combined identifier and the second combined identifier are different; and in response to determining that the first combined identifier and the second combined identifier are different, adding at least some of the second visitor data to a second visitor profile different from the first visitor profile.