Complex sentence: Pro-ana has proliferated rapidly on the Internet, with some observers noting a first wave of pro-ana sites on free web hosting services in the late 1990s, and a second wave attributed to the recent rise of blogging and social networking services.
Split into simpler sentences: Pro-ana has proliferated rapidly on the Internet, with some observers noting a first wave of pro-ana sites on free web hosting services in the late 1990s. A more recent wave is attributed to the recent rise of blogging and social networking services.