Why do I keep (all of a sudden) seeing these ads on my search engine and youtube and facebook?

This JUST started happening recently, i ran AVG antivirus but its not detecting anything... These ads keep coming up on different pages, like "Mom turns skinny in 4 weeks." ad, and the others as follows in the links below:

http://postimg.org/image/ioow8l5ln/\

http://postimg.org/image/prw9h2ziv/

http://postimg.org/image/94onoeb8j/

?2013-04-17T15:49:16Z

Favorite Answer

Install Adblock Plus :: Add-ons for Firefox
-https://addons.mozilla.org/en-us/firefox/addon/adblock-plus/

Adblock Plus for Chrome
-http://adblockplus.org/en/chrome

restart browser