Some people believe that spying is part of the succesfull thug attacks, others question that with reason. Confirmation is very hard to achieve. Especially since succesfull enemy spy attempts are not displayed so cannot be confirmed.
(Note: So far doenen and zentani have affirmed that successful spying contributes to Infamous. We deduced this from getting the achievement when neither of us had been robbed, intimidated or vandalized recently. Seeing as I [doenen] got the achievement around lvl 600, it is highly unlikely that I was attacked 1000 times en route.)
Reward: one-time use defensive boost (lasts for 7 game days)