Which of these updates is specifically targeted towards sites using spammy SEO tactics?

Google Penguin is designed specifically to penalize websites that employ manipulative and spammy SEO tactics, such as keyword stuffing, excessive link exchanges, and other deceptive practices aimed at artificially improving search engine rankings. This algorithm update focuses on identifying and lowering the rankings of websites that violate Google's guidelines on web quality and link building.

The aim of Penguin is to ensure that the search results prioritize more reputable and relevant content while discouraging those tactics that can lead to a poor user experience. Therefore, sites that engage in dubious SEO techniques may find themselves adversely affected when Penguin is in effect, leading to a decrease in their visibility on search result pages.

In contrast, the other options address different aspects of SEO and website quality. Google Panda focuses on content quality, Google Pigeon relates to local SEO and improving location-based search results, and Google Mobile Friendly addresses the optimization of websites for mobile devices. Each of those updates serves a different purpose and does not specifically target spammy SEO tactics in the way that Penguin does.