This is probably an uncanny coincidence but my Hotmail account was hacked about a week after I bought my WP7 phone and set my Hotmail account on the device. I dot actively use my Hotmail account, and only set it up so that I could upload pictures to SkyDrive. I also installed two applications from the marketplace: TuneIn and Board Express.
Thank you for the responses. Being someone familiar with good password management practices, I do have a strong password. This has happened on iOS and Android before, so I was wondering if there was a possibility that a security hole in WP7 could have caused this.