I know from conversations on this forum that there are differing views about the threat of virus's and trojans on android.
Certainly, for most of us who dont use paid for 3g services we feel quite safe.
However, threats are out there and bit defender (I know they want to sell their software to us but I don't believe they would lie to do it.) have this to say:
"We’ve seen our share of malware, adware and other interesting Android threats this summer. With autumn upon us, it’s time to recap the sizzling highlights that plagued our top 10 Android mobile malware summer charts."