If you are dealing with a Cluster B disordered person, it is likely that at some point after discovery your sick spouse will "come after you" if you try to leave him or expose his illness. You should take immediate steps to protect yourself... before it becomes necessary.
This may sound like an overwhelming job if he's the family "computer expert" and you know very little. If you are unsure, enlist a computer savvy friend or hire a professional to help you.
Technology is changing all the time. Information presented below may be outdated.
If you share a computer with a sex addict, you are vulnerable. On the other hand, it is also a benefit to you because you may be able to access a great deal of information about him. If you use the same computer, he can probably access your passwords, just as you can access his. (See my page on Investigating His Trail.)
If you share a computer, I would suggest you stop using it entirely and get a different device that is yours alone. If you cannot do that, start going to the library to use a computer, and create a brand new email address.
You will want to remove all your documents from the shared computer. (You can copy these to a USB thumb drive or hard drive, for example.) Make sure you get copies of any shared documents that are important to you. You will want to delete all your account information and passwords. Make sure when you delete these, you use a "secure" delete process. (Don't just drag to the Trash and leave it there.)
You may want to install a key logger to track his activities on the computer.
If he set up your PC, or has had access to using a computer that is supposed to be for your personal use, you will want to make sure that is secure. Here are a few articles that may be of help.
Securing your computer to maintain your privacy
Malware Removal Guide for Windows
How to Remove Malware and Adware from your Mac
If any of these links are outdated, do a simple Google search to find the most current recommendations.
Lifehacker: How to protect my computers and data when someone else is using my network
Your Apple ID is handy for setting up all sorts of linkages between your devices, but if your narc shares and Apple ID and devices with you, you want to sever that tie. (If you're computer savvy, you may want to use this to your advantage, and gather information on your cheating spouse. If you choose to do that, I suggest creating a new, private Apple ID for yourself.)
Here's what Apple says to do if you believe your Apple ID is compromised
It is likely that if you have an Apple ID, this is also your iCloud account. If your iCloud account access is under a different account, you will want to make sure that is also secure.
In case you're not aware, Google and Facebook track you on the internet. Here's a good article on deleting Google tracking and search history:
How to stop Google from tracking you on the web
If you have multiple Gmail accounts, you need to delete the tracking and search history on ALL of them.
Your gmail account may have associated Google+, Google Drive or Google Calendars. You will want to check each of these to see if you given any other accounts permission to access these.
Make sure you have your own access to all shared online accounts for bank, investments, credit cards, mortgage, utilities, insurance, shopping, social security, credit checks, auto registrations... everything. If there are pdf records, download copies of everything.
Make yourself a list.
Do you have a DropBox account? Is the DropBox app on your computer or phone? Did you set up the account or did someone else set it up for you?
This is what DropBox suggests if you are worried about DropBox security:
If your computer or mobile device was lost or stolen, or you're just generally worried about the security of your account, here are some actions you can take:
Remote wipe the Dropbox folder from a device (Dropbox Pro and Dropbox Business users only)
Another option is to shut down the account linked to your computer and start a new one.
Linked In
If you have a LinkedIn account, you will want to make sure it is secure (so it cannot be hacked) and you may want to change the privacy settings if you do not want your narc to be able to access information you would rather keep private.
Set your Privacy Settings so that only Friends can view your future and past posts.
Set up Tag Review so that you have to Approve anything that someone attempts to post to your timeline.
Decide whether you want to Block or Restrict your narc, his family and friends. I have mostly used Restricted lists to prevent my ex and his sympathizers from seeing what I post. If I Blocked him, I wouldn't be able to see what they post, and I prefer to keep tabs on them. For some women, however, this could also be a trigger. Use your discretion.
Be aware of Group Privacy Settings. Every Facebook Group you join has a certain level of privacy, and you need to be aware of it. Your comments in a Public group can be seen by anyone. Even in a Closed or Secret group, if your ex or any of his minions are members, they may be able to see your comments unless you have Blocked them.
If you tend to reuse the same email address and password (or close variations) for web account logins, you are HIGHLY VULNERABLE not only to an ex with a vendetta, but also to hackers everywhere.
"The recent "life hack" of journalist Mat Honan has demonstrated the degree to which many technology-savvy consumers have tied together numerous online services, including Gmail, Twitter, Amazon, and Apple iCloud. Due to rampant password reuse, however, attackers have been able to take passwords used on one site, and reuse them to log into a person's account on another site."
I highly recommend using software such as 1Password to create and keep all your internet passwords and account information. With 1Password, you can create unique passwords for all accounts and access these easily. I believe there are other similar (perhaps free) apps, but I have been a very satisfied 1Password user for years.
This list is by no means comprehensive. If you can think of other digital vulnerabilities I've forgotten, please send an email.