install是駭客(hackers)的動作; invade是病毒(viruses)的動作. However, the Internet also causes some problems. The main threats to Internet users are hackers who may install viruses or spyware into the users' computers. = However, the Internet also causes some problems. The main threats to Internet users are hackers who may make viruses or spyware invade (into) the users' computers. 註: into可省略, 因為invade可為及物, 也可為不及物. 參考資料:http://tw.knowledge.yahoo.com/question/question?qid=1011030917310