Your home PC is a popular target for intruders.
It is mostly not secured by an updated antivirus program, the operating system is pirated and thus does not have security patches released by the vendor, there may not be a firewall software installed.
Why do they need it?
They need hard disk space, your finance details, your processor power,etc., S/he may even want your high speed internet connection to start an attack to somewhere else, thus hiding from law agencies and putting you into legal troubles.
How do they do it?
they take advantage of a weakness in the program that is installed in your PC. They could send you an email with a link and trick you to click that, which in turn could lead you to get infected by a malware.
How do I secure?
1. Install a Anti Virus program and keep it updated with latest definition files from the vendor.
2. Keep system updated with patches from vendor, Keep utility programs like pdf readers updated.
3. Always be cautious with the emails with links or attachment. There could be emails which are phishing for an unsecured user.
4. Install a Firewall program to protect from unknown source
5. Always backup important files and folders
6. Always use strong passwords
7.Be careful while downloading and installing programs from the web.