I frequently run XoftSpy SE to check for spyware, and it often finds bs.serving-sys.com and related cookies.

I have now discovered how to block such sites within Mozilla Firefox.
First you need to click "Tools", then "Options", then select "Privacy".
Assuming that you still want to allow some cookies, tick the appropriate box, but select "ask me every time" in the scroll-down options.
"Show Cookies" then lets you see all cookies presently on the system. I suggest that you delete any that you are not totally sure about.

When you subsequently use Firefox, a box will appear whenever anything tries to install or modify a cookie. You then have options to allow or block the attempt, and further options as to whether to do so for all cookies from the site concerned, and whether to apply the rule just for the present session or until further notice etc.

The list of allowed and blocked sites is in "Tools+Options+Privacy+Exceptions", so you can review and delete any cases you desire.

I suggest that you next check back through the "Show Cookies" list, to make sure that nothing has "sneaked back in" while you were performing the above operations.

Initially, you will obviously get a lot allow/block enquiries, but you should hopefully be able to block common items like bs.serving-sys.com and quite a lot of similar spyware sites pretty fast (and also see just what your more "trusted" sites are trying to install!).

After a day or two, you can always turn off the "ask me every time" option, and just check occasionally (or through XoftSpy, Adaware, etc.) to see if anything else has "sneaked in" and should be added to the Blocked list.

There may be a similar possibility within Internet Explorer, but I only use Firefox these days!

Hope this helps at least some of you! Joe