21.  Jonathan Smith, a computer science professor and expert on network security at the University of Pennsylvania, protects his computer by closing and locking all of its doors.

22.  Just as police officers started wearing plastic gloves at a crime scene, electronic detectives now must protect computers from contamination.

23.  Larson wants to be the dominant seller of software that helps companies protect their computers from hackers and viruses as well as manage their computer networks better.

24.  Meantime, here are some common sense hints for protecting your computer from viruses and worms.

25.  Maybe a future column can offer advice to those of you who already are trying hard to protect your computer.

26.  No matter how you choose to protect your computer, you should also be sure that you back up its contents regularly.

27.  Not only will it help protect your computer, it will tell you if someone tries to break in.

28.  One Napster user, going by the screen name spyrl, described the Zone Alarm firewall software that he had installed to protect his computer from intruders.

29.  Once upon a time, in a more peaceful world, protecting your computer was smart but not all that important.

30.  Pay special attention to the links that take you to areas devoted to protecting your computer against invasion.