I get strange messages from Facebook...(SMS)?

I get updates from Facebook via SMS...and recently I've begun to receive strange symbol/number/letter combinations, quite a few of them in fact. Some are very short and just say 'Xb' or just 'X' and if there is an X it doesn't show up in my message previews. Now, though, I'm getting very long ones that say 'X '( m3(pJ@2E# ST 2" &Ey b S2| P B l<>)' and 'X #H m3(PJF@2E# SD J- eR- 8%PNp|VD KPh . ( ;tlZ I K)J> f 2A2$ h !J'. All of them start with X. Does anyone else get these/know what they mean?