Messages are encrypted

[Android Question]

Hi,

From last two days my outgoing messages are getting encrypted without my intervention.
It is showing correctly in my phone but appearing some of the text in encrypted format in my friend's mobiles.

What could be the problem, is there any virus in my mobile.

My mobile model: Samsung GT-S5830i
Andriod Virsion:2.3.6

Thanks,
Sreekanth
mail idsreekanthreddy80@gmail.com