BBC have an article about malware risk on porn sites. Whilst the article has some interesting parts....i've never use xvideos which is apparently the most popular site though it doesnt say how it defines most popular i.e visitors or unique visitors, I'm guessing they've just gone by Alexa stats which ranks it at 42 Vs. the entire web.
http://www.bbc.co.uk/news/technology-22093141