How does a virus infect you?

Viruses, worms and trojans are spread in a variety of ways. Just one person abusing the Internet i.e. sending infected jokes can bring down an entire system. Anti Virus Defence

Most people already appreciate the importance of effective anti-virus defence and have deployed some software protection. The problem is keeping protection up to date. You know that your users will forget regularly to update their signature files and all it takes is one user to destroy your whole network.