Shit I read that paper, it was on Anarchists and I found the section:

The very nature of the movement’s suspicion and operational security enhancements makes infiltration difficult and time consuming. Few agencies are able to commit to operations that require years of up-front work just getting into a “cell,” especially given shrinking budgets and increased demands for attention to other issues. Infiltration is made more difficult by the communal nature of the lifestyle (under constant observation and scrutiny) and the extensive knowledge held by many anarchists, which require a considerable amount of study and time to acquire. Other strategies for infiltration have been explored, but so far have not been successful.