Magicjack security issues

I've read a couple of reviews on the internet from people that have used the magicjack telephone system on their computers where they claim that after a time (1 to 5 months) their computer becomes overrun with viruses and trojans despite having valid windows xp pro and firewall plus virus protection. I contacted magicjack and asked them about security issues with magicjack and they deny there being any.

 

I would like to use mine, but am now fearful. I do have norton internet security 2008 on my pc. Am I fully protected while using magicjack on my pc; or does it provide security issues to the system which no one has addressed?