Hello,
There are two possibilities. One is that your account was compromised, and the other is that someone else is using your address as the From: on your address but they don't actually have access to your account.
To prevent the first possibility I recommend turning on two step authentication -
How to turn on 2 step authentication (login verification) in Hotmail
There isn't anything you can do about the second option. Hopefully these days most email services are treating email from @hotmail.com that doesn't come from the Hotmail servers as suspicious / spam.
;; ANSWER SECTION:
hotmail.com. 291 IN TXT "v=spf1 include:spf-a.outlook.com include:spf-b.outlook.com ip4:157.55.9.128/25 include:spf.protection.outlook.com include:spf-a.hotmail.com include:_spf-ssg-b.microsoft.com include:_spf-ssg-c.microsoft.com ~all"