There are 2 primary kinds of spam data you’ve probably seen show up in your Google Analytics reports. In some cases you may not have even realized it was spam:
1. Spam sites in your referral reports
It looks like this:
These are just a few of the hundreds of spam URLs you might see show up – share-buttons.xyz (actually, lots of sites with the .xyz extension), free-social-buttons, free-floating-buttons.com, copyrightclaims.org are some other common ones, but there are soooo many! Those kinds of sites look pretty dodgy from the outset and might ring some alarm bells.