Whether you are sharing your baby with your babies, or your kids have their own Mac, there are a few simple steps you can take to keep your Mac safe and keep your family safer online.

First steps – each user gets their own space.

Picture this  scenario – you loan out your laptop for a quick bit of homework.  When it comes back, the window you had open in Word contains your third-grader’s book report on “How to Eat Fried Worms“. The fiscal-year summary you’ve been slaving over for the boss? History. All those icons that cluttered the desktop? History. Tax return you were working on (one of those icons)? History.

If you setup everyone with their own desktop, they leave your stuff alone, you leave theirs alone, everyone gets along.

This is *very* easy to setup, especially if you do so early on.

Step 1: Setup the accounts

  A.  Open System Preferences (from the dock, in Applications, or under the Apple menu top left of the screen). Click on “Accounts” or “Users” or “Users & Groups” (varies, based on which version of Mac OS X you are using.

If it says at the bottom “click here to make changes”, do so, and enter your password. This is the one you enter when you install programs, do updates, or when you first set up your Mac.

  B. Add a user.

Click the plus sign (lower left portion of the window), and enter a name for the new user account and give it a password. (Note: Do *not* check the “allow user to administer this computer” button).  Click “Ok” or “Create User” to save your work.

Don’t get too creative here – each person’s actual name is fine. If you’re setting up to share this with your kids, have them help you pick a password. It should be something they can remember, and you should write it down (see “Should I Know my Kid’s Password”). For younger kids, even “cat” is fine. Just the fact that there is a password helps keep everyone segregated. Not only do you not want the kids logged in to your account and messing up your files, you don’t want your spouse inadvertently saving files on the kids’ desktops and then being unable to find them later.

  C. Add more users.

Repeat the above for each additional user. I also like to add one for “everyone else” to use, for when Uncle Marty comes over.

2. Make it work automagically

Now we set things up to keep everyone from inadvertently logging in as someone else.

If you haven’t yet created additional users on your Mac prior to this, it will likely be set to log in automatically. Under the list of users in System Preferencs->Accounts, click on “Login Options”, and set “Automatic Login” to “Off”.

Last, set it so you can ‘sleep’ the Mac, or walk away and have it lock the screen after a short while. Still in System Preferences, click on “Show All”, then on “Security”.

Set “Require password after sleep or screen saver” to “Immediately” or at least a short interval.

Then, set the machine to lock after inactivity. You can do this either in ScreenSaver or in Energy Saver section of System Preferences. Set the “display sleep” in Energy Saver, or the “Start Screen Saver” in Screen Saver preferences to a small number – just a few minutes, usually.

Stay tuned for “Thoughts on Kids: Passwords, Rights and Responsibilities”!

Everything she clicked on – internet, email, docs – refused to work. Instead, she’d get a popup message with a rather cryptic (yet more informative than most) error: “Program name Bad image C:\windows\system32\0020.DLL is not a valid windows image”.

It turns out this was a symptom of a rather badly written little piece of malware. I say this, because if a virus, spyware, or adware disables a computer, the first thing a user will do it get it fixed. Really, folks. If you want to write good viruses which actually do their jobs (usually sending masses of spam) then make them do it without visible effect.

But I digress. I did a bit of searching, and found a fix. We couldn’t just run a virus-checker, since that did nothing but produce the “not a valid windows image” error. This one required manual termination.

I fixed this one over the phone, walking the client through it step by step. Normally I try not to do [tippy title="registry" reference="http://en.wikipedia.org/wiki/Windows_Registry" ]The Windows registry stores configuration and preference settings for the entire system – programs, settings, just about anything that can be changed.[/tippy] edits over the phone, since there is a good chance of miscommunication, thus making things worse. In this case, though, they were an hour away, during rush hour, so the phone seemed the best option.

We had to do two things – remove the registry entry that caused 0020.dl to run, and remove 0020.dll itself.

First, we got rid of the file. (We couldn’t edit the registry first, since we got the error when we tried to open [tippy title="regedit" reference="http://en.wikipedia.org/wiki/Regedit#Editing"]regedit.exe is the program in Windows that can be used to manually edit the registry. Most changes to the registry are made behind the scenes, usually when programs are installed or settings are changed in the Control Panels.[/tippy].

To remove the errant file, we opened up “My Computer”. In “My Computer”, we opened the hard drive (“Local Drive (C:)”). At this point, Windows warns, something like this: “Do you really want to do this? The contents are normally kept hidden”. We said yes. We then continued deeper into the system, double-clicking on the Windows folder, and then on system32. You might recognize this as the path that was in the original error message – “C:\windows\system32\0020.dll”.

Once we were in the system32 folder, we looked through the list and found 0020.dll. I wanted to remove it, and any other files in this folder that were created at the same time. We found one other file called “WORK.DAT” that had the same “date created”. We threw both files away.

Now that the file was gone, we could again open programs, so we opened regedit (Click “Start”, then type “regedit” in the search box, and hit return in Vista or Windows 7, or if you’re in Windows XP, click Start, then Run, then type regedit, and hit return).

In regedit, there is a list of items on the left, all starting with “HKEY_”. We opened the HKEY_Local_Machine folder by clicking the plus sign next to it (it’s a triangle instead of a plus sign in Windows 7). Then, in the list of items under HKEY_Local_Machine, we found “Software”. We opened that one, then “Microsoft”, then looked for “Windows NT”, then for “Current Version”, then finally in “Current Version”, we looked for and found “Windows”.

Now we were here, in the registry hierarchy: HKEY_Local_Machine\Software\Microsoft\Windows NT\CurrentVersion\Windows . In the right-hand pane of the regedit window, we could a list of items. One in particular, we needed to change. Doubleclick on “AppInit_DLLs”, and we saw that it had a value entered of “C:\windows\system32\0020.dl”. We highlighted this and hit “delete”, then clicked “ok”. Then we restarted, and all was well.

As a final step, I had them fire up their antivirus software and update it, then run a full scan.