What kind of router do you have? If it's a Linksys router you could be in danger from new malware that attacks your firmware and replicates itself. It's called "The Moon" worm after these weird images inside the code from the movie Moon.
This worm was discovered by Johannes B. Ullrich, Ph.D. of the SANS Technology Institute. He identified the vulnerability in 11 specific models, though it could exist in many more depending on firmware version. Here are the models:
E4200, E3200, E3000, E2500, E2100L, E2000, E1550, E1500, E1200, E1000,E900
If you have a Linksys router, I highly recommend you update your firmware immediately. Each router is different, so you'll need to read your router's user manual to find out the specific process.