I believe they use Facebook's open graph API to scrape data. Facebook has been known to shut down access when you're taking too much information too fast without notifying them (as in the case of Twitter and Ping), but I imagine Greplin will take the time to notify Facebook of their intentions when before this becomes an issue.
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Is Greplin mostly screen scraping your sites? I imagine there's a lot of data that people want to search that isn't available via the various APIs.
What happens when Facebook tells them it is against the TOS?
I believe they use Facebook's open graph API to scrape data. Facebook has been known to shut down access when you're taking too much information too fast without notifying them (as in the case of Twitter and Ping), but I imagine Greplin will take the time to notify Facebook of their intentions when before this becomes an issue.