Someone just hacked my webcam!?

Okay i was browsing yahoo and i see my webcam light come on and i close my laptop. i was like what just happened! and my laptop went to sleep so it turned off but when i thought it was safe to go back i turned on the laptop and the light came back on! i covered the camera with my thumb and after a minute of searching what was going on it turned off. i didnt have any other tabs open except yahoo. i saw that they could like go through your entire computer and im worried cause i have my credit card information saved on documents and some pictures from girls that have sent me. what should i do! how did this happen. i only remember trying to download a app for a game but most of them ddnt work but i ddnt delete them until now..,. thank you