There is a security risk with using an operating system after its end of life, and that risk is not recommended. It's relatively safe soon after EOL, especially for users as opposed to businesses and schools, but the longer one waits, the higher the risk. I definitely wouldn't recommended using Windows XP. Other compatibility issues aside and only talking about security, it's pretty exploitable. It only takes one malicious website or even advertisement, particularly with an outdated browser too on top of it.