Alex, I had the exact same issue happen on the 8th. Messages were sending from my phone every 30 seconds or so. I called my service provider and they recommended I change my phone number as they did not know what was happening--huge hassle (and $35 charge), but I did. Now this morning, March 10th, it happened again. When I checked my phone this morning, it said my Apple ID had been used on a new iPod touch. So, I promptly changed my password. I'm concerned now about charges to my Apple account or cell bill... as well as privacy in regards to banking info, passwords, etc.
Has it happened to you again since the 7th? My message looked similar to yours. "I" was sending it to numbers in China, and when I put the text into Google translate, it was something about knock-off purses for sale...