to secretly become part of a group in order to get information or to influence the way that group thinks or behaves

A journalist managed to infiltrate the powerful drug cartel. 一位记者设法打入了势力强大的贩毒集团内部。

to move slowly into a substance, place, system, or organization

At about this time the new ideas about "corporate management" had begun to infiltrate (into) local government. 大约此时，有关“共同管理”的一些新思想逐步开始为当地政府所接受。