Those advertisements that one sees plastered all over the websites you visit are not only distracting, they can link to malware too.
Adobe Flash is often used for displaying advertisements and is one of the most exploited ad delivery mechanisms that exist. Just do an Internet search for “Flash exploit” to see what I mean.
A particularly nasty bit of work called Cryptowall is making the rounds. In a nut shell it encrypts your files so you cannot open them and demands payment for unlocking them.
You might want to think twice before clicking on the adverts on web pages or better still block adverts with the hosts file on your device.
A good source of up to date hosts files can be found here http://pgl.yoyo.org