The most popular open-source software is also the most free of bugs, according to the first results of a US government-sponsored effort to help make such software as secure as possible. The so-called LAMP stack of open-source software, which includes the Linux operating system, Apache Web server, MySQL database and a scripting language--PHP, Perl or Python, has a lower bug density -- the number of bugs per kilolines of code (defects/kloc) -- than a baseline of 32 open-source projects analysed, Coverity, a maker of code analysis tools, announced Monday.