Google's internal spy system was Chinese hacker target (2010)
zdnet.com
zdnet.com
Here is a much more recent report on what likely actually went down: http://arstechnica.com/security/2013/05/chinese-hackers-who-...
tl;dr: it's speculated that they were interested in who the US government was watching as any overlap with their own operatives meant that they were likely compromised.
[1] http://www.computerworld.com/s/article/9144221/Google_attack...?
https://en.wikipedia.org/wiki/Greek_wiretapping_case_2004%E2...