Due to privacy and information security issues, it is important that you keep tabs on who is using your computer. Identity theft alone costs businesses and individuals over $56 billion dollars per year. Your computer contains an abundance of information about you, including the sites you have visited, bank account information that you have saved in files for references, and even usernames and passwords.
Install tracking software onto your computer. This software is commonly used by employers who want to monitor the Internet use of their employees on company-owned computers and parents who want to know what their kids are doing online on the family computer. Some software programs will also notify you via email or text message when your computer is connecting to the Internet and when someone is visiting certain sites.
Go to your Internet browser and check the history. If you don't recognize some of the sites that were visited, it's likely that someone else has been using your computer.
Go to popular websites that require you to login, such as Yahoo!, Google, Facebook and Myspace. Click inside of the form boxes to see if another person's username appears in the drop down box (this method will only work if your browser is set to save all form data).
Open Windows Explorer and click the "Search" button on the menu bar. Choose "All files and folders" and select "My Computer" from the "Look in" drop down box. Click the "When was it modified?" arrow and select the specific dates that you suspect someone was using the computer. Then click "Search" to view all the files, folders and programs that were opened on that day—if you don't recognize some, then you know that someone else was using the PC.
Go to the Start menu and click "Run…" Type "eventvwr.msc" (no quotation marks) inside the box and then "OK." This will bring up a program called Event Viewer, which can show you all of the most recent events that have occurred on your computer along with the dates and types. Click any of the categories (usually Application or System will reveal the most useful data) and view the most recent activity.
Set an administrative password that requires users to log onto your computer to use it. To do this, go to the control panel and click "User Accounts." Either choose "Create an Account" or click the existing "Administrator" account to set a password for login.
These methods work for Windows operating systems.
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