Modern high-speed modems are susceptible to electrical surges carried over the phone lines.
Power surges, often caused by lightning strikes can cause a modem to stop functioning properly.
Telephones and fax machines are generally not as susceptible to these power surges, but modems are designed to protect the rest of the computer system from damage in the case of such a surge. Protecting the rest of your computer from further damage is an industry standard. Any damage caused in this fashion is not due to a defect in manufacturing, and is not covered under warranty. It is important to protect your system by connecting the modem to the wall jack through a surge protector that includes phone line surge supression so that your modem and computer will be protected from damage. Getting high connection speeds out of your modem is dependant on several conditions.