Threats while P2P File Sharing

I am new to networking. Normally my work is to share files on computers connected in network. But the thing is that I am facing problem while sharing file on network. The most common problem I am facing is of virus and worms. If one computer is infected with virus all the other computers connected in network are catching the same virus or worms. I am facing the other threats but I am not getting the exact words to define the problems. Can anybody help me in knowing the threats while p2p file sharing and the solutions for same?

If you think sharing file on network is safe, then you are wrong. There are many malware writers who are aggressively using the shared network for spreading the virus and worms. So you have to have to very careful about the files and software downloaded from unknown source. Downloads from these sources potentially infecting the peer to peer network. Normally most of the peer to peer file sharing programs is made in such a way that they can automatically replicate and launch at startup and also configure the computers connected in network. This process makes your network vulnerable to threats.

Some of the threats faced by computers connected in network are as follows:
1. Poisoning attacks: In this type of attack, attacker exploits the flaws in Domain Name
System software. If the Domain Name System Software is correctly validated attacker can spoofs the Internet Protocol address and Domain Name System entries for a target website or Server.
2. Downloaded files may be infected with virus and some software’s are designed in such a way that they can harm your data. Means altering your data, deleting your data, or copying confidential information from your computer. These types of viruses are called Trojan.
3. Tracking the user’s id and harassing them or illegally attacking them is also a problem. These types of attacks are normally called “Identity Attacks”

If you are dealing with network security issues then you must have knowledge about “Spam, Theft of data, Viruses , Denial of Service attacks or Distributed Denial of Service attacks, Trojan Horses, worms”. Worms are malicious programs that spread to maximum number of computers connected in network. They can use the different procedure to spread from one computer to other. They are normally spread through attachments in mails. So if you are getting any attachments from “Unknown User”, try to avoid downloading of those attachments. Regularly scan computer with antivirus software’s and do not forget to update antivirus software.

The guy, is asking for any solutions how to stop Network threatening...
Which are the steps he should have in mind?