Social network aggregator Power.com, which Facebook sued in January for the way it accessed and stored Facebook user data, has counter-sued Facebook for “anticompetitive practices” in US Federal District Court in Northern California.

At the heart of the matter is whether Power.com should be allowed to store Facebook users’ credentials and “scrape” their Facebook data without using authorized Facebook APIs and programs like Facebook Connect. Facebook says doing so violates the Facebook Terms of Service and threatens user privacy and security, and sued Power.com in January after it refused to change its site after several weeks of direct discussions with Facebook.

In its response and countersuit today, Power.com is essentially claiming that the court should force Facebook to allow Power.com to scrape and store user data because 1) doing so is “common industry practice” (citing Facebook’s own contact importer), 2) Facebook’s own terms of service say Facebook doesn’t own user data, and 3) Facebook’s behavior in not allowing it to do so is “anticompetitive.”

Facebook’s original lawsuit also claimed that Power.com also falsely signed emails it sent as “The Facebook Team” from “facebookmail.com” during a promotion in which it was offering $100 to the person that invited the most new users to Power.com, but Power.com does not appear to be countersuing against that claim.

According to web metrics firm Compete.com, US traffic to Power.com has decreased to 14K uniques in June after its peak in December at 100K uniques. 91.7 million people visited Facebook.com in June.

We think the courts will side with Facebook in this case - even though Facebook is aggressively fighting attempts to access Facebook user data that don’t fall within Facebook’s authorized APIs, it’s premature to apply antitrust laws to Facebook today. Nevertheless, we’ll continue following the case, as it will set an important precedent for similar cases dealing with access rights to sensitive user data in the future.