A dangerous misconception is that dynamic IP (common with PPPoE) makes you more secure. While it does make it a bit harder for someone to find you, it provides little real protection against common forms of Internet attacks and abuse.

In addition, while you are protected from the outside when PPPoE is disconnected, you may still be compromised from the inside by a worm or virus. (Microsoft Windows in particular has exploitable weaknesses and vulnerabilities.) Fortunately, it's relatively easy to mitigate those risks:

• Personal firewall software: The use of personal firewall software is strongly recommended. Products such as ZoneAlarm and Tiny Personal Firewall are both free and effective. They are even recommended if you have a router -- the router may protect against inbound attacks, but personal firewall software can provide additional protection against outbound attacks (from a worm or virus). Current anti-virus software is also strongly recommended.
  
• Router: Popular DSL routers such as the Linksys BEFSR11 or BEFSR41 not only facilitate PPPoE and connection sharing, but also provide security protection, by means of NAT (the most common sharing mechanism), firewall blocking functions, or both.