Go to Blackerry App world and download Lookout Mobile Security.It's free, it has antivirus software,backs up your phone contact info etc and it has phone location software built into it to help locate a lost phone.
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Technically it can't "get" a virus but it could become a carrier and infect your pc. Especially if you are frequently transferring media files back and forth. Personally I have never concerned myself with the possibility. As long as your pc has anti virus software installed.
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