A surge protector is an appliance or device designed to protect electrical devices from voltage spikes, which is most used in places without lightning protections, like houses and villages.
A voltage spike typically lasts 1 to 30 microseconds, that may reach over 1,000 volts. Lightning that hits a power line can give many thousands, sometimes 100,000 or more volts. A motor when switched off can generate a spike of 1,000 or more volts. Spikes can degrade wiring insulation and destroy electronic devices like battery chargers, modems and TVs.
Spikes can also occur on telephone and data lines when AC (alternating current) main lines accidentally connect to them or lightning hits them or the telephone and data lines travel near lines with a spike and the voltage is induced.
A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting current to reduce the voltage below a safe threshold. Blocking is done by using inductors which inhibit a sudden change in current.
Also, if you consider using powerline adaptors for networking, please use the non-surge-protected sockets instead.