Inquisitive minds wanting more information should be directed to StarForce.RE.Tools.ReadNFO-RELOADED - http://www.glop.org/files/rld-sfrt.rar (sorry for the hotlink!) - for a detailed technical analysis published concerning the StarForce 3 protection. A fine piece of work, if I may say, though I shall not identify the authors.
StarForce 3 was really quite intrusive, including secretly-installed ring0-access device-drivers. Flaky and damaging to the security of your system and very widely complained about.
I would not say such a monstrosity is an achievement UbiSoft should be proud of: indeed, they actually apologised, although I would not say they were genuinely sorry in any sense.
I would like to thank the developers working on the actual game, of course. I feel sorry for them that the publisher had such strong opinions about that.