Yahoo! said it believes 16 patents held by the Internet giant have been used in Facebook’s data centers and servers, according to a regulatory filing made by Facebook.

The social media company alerted the market of its share price for its upcoming IPO, which valued the company between US$85bn and $85bn yesterday. In its document filed with the US Securities and Exchange Commission, however, it sought to alert shareholders of possible risks that could affect the company.

“We received a letter dated April 23, 2012 from Yahoo indicating that they believe 16 patents they claim to hold may be relevant to open source technology they allege is being used in our data centers and servers,” the document said.

“Yahoo has not threatened or initiated litigation with respect to matter described in this letter but it may do so in the future.”

It said Yahoo! had already filed a lawsuit in the US District Court for Northern California alleging a number of Facebook product infringements, in particular 12 patents relating to advertising, social networking, privacy, customization and messaging.

“We filed our answer with respect to this complaint and asserted counter claims that Yahoo’s products infringe ten of our patents,” Facebook said.

“This litigation is still in its early stages and the final outcome, including our liability, if any, with respect to Yahoo!’s claims, is uncertain.”

Facebook warned any impact could be material to the business, and financial conditions and results of operations at the company could also feel the strain.

Facebook hinted that the number of claims being made against the company in regards to IP is expected to rise.

“We expect the number of patent and other intellectual property claims against us to grow,” Facebook said.

It also warned that some final outcomes have the potential of ending with an injunction for Facebook to cease some or all operations.

Facebook started the Open Compute Project, which aims to share knowledge for the benefit of efficient computing, just over a year ago.

“We decided to honour our hacker roots and challenge convention by custom designing and building our software, servers and data centers from the ground up – and then share these technologies as they evolve,” the Open Compute Website says.

Since then, Open Compute has attracted a number of big data center and technology  players to the cause including Rackspace and Red Hat and has showcased technologies including its custom-built servers.

Many in the industry have said the project has the power to revolutionize the way efficient data centers are built.