I've never really had ics as my android os for a long time, so i don't know about it getting any viruses in that os. But as far as jb goes, never encountered anyvmalware!
Might i suggest (even though i'm not directly answering your question) if you fear for your battery life you follow these steps:
-get a higher capacity battery. (I got a chinese, i think, one off the internet with 2850mAh capacity and it works just geat. Batrery+charger good for all i9300 batteries=15€. if ur in america u can probably get less. And for just the vattery even less. And i've also seen 3100mAh batteries, since mine is GREAT these must be like portable energy source XD)
-change kernel (need root. I suggest siyah kernel, as most stable. It also makes your phone faster without absorbing more battery, it instead safeguards battery life).
-change rom (need root. I suggest foxhound rom, very good with battery life, can't complain. While aosp roms tend to suck the life out of i9300, samsung based ones are more stable, so if you gotta choose, choose sammy
--(if you're really paranoid about battery life)it requires root. Downclock cpu, or change cpu gorvernor (manager for cpu frequency on android. There are many different profiles, some aggressive some just want to save your battery life. More battery=slower cell).
Hope i helped:thumbup:
Sent from my GT-I9300 using xda app-developers app