In the past, websites have not generally made the user explicitly aware of the storing of cookies, however tracking cookies and especially "third-party tracking cookies" are commonly used as ways to compile long-term records of individuals' browsing histories — a privacy concern that prompted European and US lawmakers to take action in 2011. Cookies can also have implications for computer forensics. In past years, most computer users were not completely aware of cookies, but users have become conscious of possible detrimental effects of Internet cookies: a recent study done has shown that 58% of users have deleted cookies from their computer at least once, and that 39% of users delete cookies from their computer every month. Since cookies are advertisers' main way of targeting potential customers, and some customers are deleting cookies, some advertisers started to use persistent Flash cookies and zombie cookies, but modern browsers and anti-malware software can now block or detect and remove such cookies.