There's speculation that Schema.org may have been compromised in some manner. A number of people (including myself) have noticed some very spammy links showing up in Webmaster tools as Itemtypes under Structured Data.
Rather than displaying (for example) http://schema.org/SiteNavigationElement, there's an itemtype pointing to various URLs on domains including www.yalwa.com, locanto.fr and askalo.fr. The only thing any of the sites have in common is their use of Schema.org.
Curiously, you can also reproduce the issue using the Structured Data Testing Tool and entering a small HTML snippet. The issue only seems to be affecting those in Europe though, with US users only able to reproduce by using an EU based proxy.