This evil consists of hackers and slashers. First of all slashers are people that upload viruses in to the consoles update stream. These viruses tend to take control of the consoles hard drive and could spy on your game or even join it as a NPC.
Hackers are just about the same, but they just want free stuff even if it means getting put in prison for life. Hackers can steal your saved game credits and use it for their own enjoyment. Yes I know this really hurts if this ever happens to you. I have never had one of these because I don't leave my internet running on my console.
I also didn't have to encounter these, cause I have an xbox 360 and it is partly run by Microsoft which makes an extra feel of security. Most of gamers out there who have a play station3 are more prone to encounter one of these and not know that they own one. So the safest joice would be an xbox 360.