If you're a DSL customer and use a D-Link DSL-2740R model, then you're vulnerable to a proof-of-concept discovered by Bulgarian security researcher Tondor Donev. The attack allows hackers to bypass the router's security and hijack Web traffic.
The router was released in 2009 and the security flaw is present in ZynOS, firmware installed on the router. The router has been phased out, so if you've purchased a router recently then you probably don't have to worry.
Breaches like this don't just affect people who own the router. Hackers can exploit these security holes surprisingly easily.
How they do it might surprise you.