Creating a Forum with phpbb is safe ?

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I had 2 websites which run under wordpress,recently I bought a domain and planning to build forum for that domain.But I'm stuck up here because i'm in great confusion in choosing Best forum software.My friends Referred vBuletin as the best forum making software. But $160.00 to buy it's license is huge,i have to cut my mouth for few days. So i decided to go for free software,then i found Phpbb .But i heard alot about phpbb flaws,because it is opensource ,meaning anybody can look at how the board is constructed and add or bild it.This is main problem becoz since anybody can view source code. Please suggest me whether to choose phpbb or VBuletin ?