not exactly as you can see :) ... you kill the last 3 positions with dividing by 1000 and round the result ... that gives the chance to be not unique when its called too fast ... try it ;)
hmmm ... i don't know ... to be sure the timestamp is always unique ... even a random number might have a chance not to be unique ... but in case you want to have a 'pool' of numbers then you may create a list with numbers that you may assign to a user each time ... and assign that only once ...
nope it is nothing security relevant
i am using this for behavioral targeting
if i get a unique visitor number i might be able to track them
and with so many request on server engine i cant use it to set a unique number every time a visitor visit the websites as it will increase the load
i see ... so you assign the id to the user and track his behaviour with this id and may be he is getting proposals or special links or interfaces depending on his behaviour? :) ...
good luck with your project ... and post back to the forum anytime you have more questions,