I was going through a Google analytics report yesterday - and was horrified! It showed pages on our website that CLEARLY weren't ours. Then I went through other client's analytics - same thing.
Likely, if you are using Google Analytics to monitor your website, you are seeing this too. I've seen a dramatic uptick in this since April 15. Based on the buzz online, others are too.
If you see pages listed in your analytics that you find offensive, don't worry. Your site has not been hacked*, and no one suspects you of a hidden life. This is not helping or hurting your SEO. Google isn't punishing you for this. However, it does mess with your ability to interpret the data in your analytics report.
There are debates as to the best options to tackle this, and those options can be limited, based on the hosting platform on which your site sits.
Obviously, DO NOT FOLLOW/ CLICK ON THE LINKS!
Here is an example of strategies to clean this up (third party site). In short, there is Ghost Referrer Spam and Crawler Referrer Spam.
If you are interested in having us take a look and help clean up (what we can), let us know. If you want to follow the instructions in the linked article, great!
If you have additional recommendations, I'd love to hear them.
*I added the asterisk because, there is always a chance that your site has been hacked...but don't assume it was, is my point.