Cookies are messages that web servers pass to your web browser when you visit Internet sites. Your browser stores each message in a small file, called cookie.txt . When you request another page from the server, your browser sends the cookie back to the server.
Cookies that are sent over HTTP (port 80) are not secure as the HTTP protocol is not encrypted. Cookies sent over HTTPS (port 443) are secure as HTTPS is encrypted. So, if Facebook sends/receives cookies via HTTP, they can be stolen and used nefariously. That’s why you should always check for a green padlock right beside your browser’s url bar. A website without a green padlock is insecure and all data that are sent and received can be hijacked with Man-in-the-middle attack.
No, cookies are stored in txt files which will never cause any trouble to your device.