When some users choose to disable HTTP cookies to reduce privacy risks as noted, new types of cookies were invented: since cookies are advertisers' main way of targeting potential customers, and some customers were deleting cookies, some advertisers started to use persistent Flash cookies and zombie cookies. In a 2009 study, Flash cookies were found to be a popular mechanism for storing data on the top 100 most visited sites. Another 2011 study of social media found that, "Of the top 100 web sites, 31 had at least one overlap between HTTP and Flash cookies." However, modern browsers and anti-malware software can now block or detect and remove such cookies. This study shows how the two different types of cookies commonly exist in popular visited websites. For the users who choose to disable HTTP cookie, flash cookies could very well still exist if the two cookies overlap for a specific visited website. -->