As I wrote about a couple of weeks ago, Yahoo!’s (YHOO) patent portfolio is one of the least talked about aspects of the whole takeover speculation surrounding the company.  Yet, one of the greatest at-risk targets of an offensive owner of Yahoo!’s patent portfolio could be Facebook.

With Facebook rumored to be eyeing a $100 billion IPO sometime next year between April and June, anyone who wants to have maximum leverage against Facebook would seem to want to act now — just as Yahoo! did in 2004 against Google (GOOG) just prior to their IPO.

Back in 2004, Yahoo! would probably be the first to admit it left an enormous amount of money on the table — especially by today’s standards — when they struck a deal with Google 3 weeks before their IPO around their paid-search patent (No. 6,269,361).

Yahoo! could have sought an injunction to halt the entire AdWords paid search business model.  That business model makes up the large part of what is now a $29 billion a year business.  Instead, Yahoo! agreed to a modest amount of Class A common stock which they promptly sold in August and September 2004  – back when Google’s stock was hovering around $100/share (whoops).

If Yahoo! had known then that they could have shut down what was going to be a $30 billion business in a few years down, would they have?  Arguably, if it had happened, Yahoo! would still be the leader in search today.  Would they at least have held out for a king’s ransom from Google?  They certainly should have.

Well, fool me once, shame on you; fool me twice, shame on me.  It’s not often in life you get a do-over.  Yet, that seems to be exactly what Yahoo! might get with the upcoming Facebook IPO.

Yahoo!, as of today, has 955 granted patents according to the US Patent Office.  These patents are in the areas of paid search, display, and social networking (among others).  By comparison, Google, before their deal to buy Motorola Mobility (MMI), had 925 granted patents.  LinkedIn (LNKD) has 1 granted patent.  Groupon (GRPN) and Zynga have no granted patents.

Facebook has 161 granted patents to date — all granted since April 2009 as the company has been feverishly working to catch up in this acknowledged weak area of IP.

Many patent lawyers will tell you that you never know the value of a patent until it is tested in court.  Yahoo!’s 6,269,361 patent was tested several times before the Google deal in court.  It won’t expire until July 31, 2018 and is likely going to be valuable against Facebook (as well as Microsoft (MSFT) if Yahoo! ever terminates its search deal which agrees to share intellectual property between the two companies).  There are likely other patents (at least 5 – 10 out of 955 granted) which can be used offensively against Facebook in addition to the patent.

via How Yahoo! Could Trip Up Facebook’s Grand IPO Plans – Forbes.