There are plenty of computer programs that allow you to control or to access your desktop or other computer when you are visiting a client, residing at home, on vacation, and so forth. These programs, such as logmein or gotomypc actually work quite well so that you are able to essentially get inside your main computer and copy files, manipulate files, utilize files and programs, and overall to conduct work as if you were actually in front of your main desktop. There are other utilities that one can use for peer-to-peer (P2P) file sharing which allows you to share files such as music, picture, or video files, from one computer to another. All of this appears pretty wonderful, the fact that you can share or swap files remotely and routinely, work on tasks remotely, and so on, but this assumes that you live in a Mr. Rodgers type of neighborhood but in fact, you don't.
Anytime that you open up your computer to remote control access or to P2P sharing, you have basically opened up Pandora's Box, and things that you think are under your control, are not. Sure, there are always controls, protocols, security codes, crosschecks, and so forth that will in theory protect your information and ensure the integrity of your computer, but all of these can be compromised. Every P2P network as well as remote access programs will tout its protections and integrities, but they are all vulnerable to hackers that know how to exploit them and once a hacker gets into your computer through security leaks or bots or through cracking passwords or through malware, your files are vulnerable to being copied and exploited.
As bad as remote control access and P2P networking can be to the integrity of your computer and to yourself, the simple fact that you utilize the internet, and further that your internet is up 24 hours/7 days a week, means that your entire computer and its contents are vulnerable to being exploited and attacked at any moment, whether that attack is done through a backdoor malware attachment, a network phishing expedition, a "false-flag" website that will initiate malware, or a peripheral device setup to look and behave normally but containing malicious software that activates upon installation.
The basic fact is that once your computer is accessed by an outside computer, whether intentionally or not, that monitoring computer will through a skilled technician hands have the ability to wreak havoc within the subject computer itself, to which it can monitor, copy, or compromise the target computer as if it was by actuated by you, or perhaps the attack will be considerably less invasive depending upon a multitude of conditions and efforts submitted. This in essence means that any government agency, foreign or domestic, or criminal consortium, or hacker can in all probability readily keep track or compromise your activities on your computer, the websites that you visit, along with the documents that you create, both private and confidential, the web chats that you have, and the exact identity of who and what you are.