The following table summarizes warrant activity for the years ended December 31, 2014, 2013 and 2012 (number of shares in thousands):

January 2013 Financing – In connection with the January 2013 Financing Transaction, the Company issued warrants to purchase an aggregate of 1,708,700 shares of common stock. All of the warrants were exercised in 2014.

Series A and B Notes – In connection with the Company’s issuance of its Series A and B Notes, the Company issued warrants to purchase up to 788,400 and 1,051,200 shares of common stock, respectively. All of the warrants were exercised in 2014.

September 2012 Public Offering – On September 26, 2012, the Company raised $10,091,000, net of $909,000 of underwriting fees and issuance costs, through a public offering of units consisting of an aggregate of 1,833,000 shares of common stock and warrants immediately exercisable to purchase an aggregate of 1,833,000 shares of common stock at an exercise price of $8.85 per share and which expire in September 2015. The Company accounted for the net proceeds of the offering by first allocating the $1,658,000 fair value of the warrants to liabilities and then allocating the remaining amount to equity. As of December 31, 2014, warrants to purchase 473,000 shares of common stock remained outstanding.

July 2012 Public Offering – On July 3, 2012, the Company raised $10,903,000, net of $1,137,000 of underwriting fees and issuance costs, through a public offering of units consisting of an aggregate of 1,867,000 shares of common stock, warrants immediately exercisable to purchase an aggregate of 1,867,000 shares of common stock at an exercise price of $9.45 per share and which expire in 2017 (“Series I Warrants”) and warrants immediately exercisable to purchase an aggregate of 933,000 shares of common stock at an exercise price of $7.95 per share and which expire in 2014 (“Series II Warrants”). The Series I Warrants and the Series II Warrants are subject to “weighted-average” anti-dilution adjustments if the Company issues or is deemed to have issued securities at a price lower than their then applicable exercise prices. Due to subsequent transactions, the exercise price of the Series I Warrants was reduced to $6.09 per share and the exercise price of the Series II Warrants was reduced to $5.47 per share. The Company accounted for the net proceeds of the offering by first allocating the $3,380,000 fair value of the warrants to liabilities and then allocating the remaining amount to equity. The Series II Warrants expired unexercised. As of December 31, 2014, Series I Warrants to purchase 211,000 shares of common stock remained outstanding.

Warrant Inducements – During 2014 and 2013, certain holders exercised warrants and received payments from the Company in the aggregate amounts of $2,271,000 and $785,800, respectively, in cash as an inducement for these exercises, which were recorded as an expense.

Warrant Terms – The exercise prices of the warrants described above are subject to adjustment for stock splits, combinations or similar events, and, in such event, the number of shares issuable upon the exercise of the warrants will also be adjusted so that the aggregate exercise price shall be the same immediately before and immediately after the adjustment. The warrants generally require payments to be made by the Company for failure to deliver the shares of common stock issuable upon exercise. The warrants may not be exercised if, after giving effect to the exercise, the investor together with its affiliates would beneficially own in excess of 4.99% of the Company’s outstanding shares of common stock. The blocker applicable to the exercise of the warrants may be raised or lowered to any other percentage not in excess of 9.99%, except that any increase will only be effective upon 61-days’ prior notice to the Company. If the Company issues options, convertible securities, warrants, stock, or similar securities to holders of its common stock generally, each holder of certain warrants has the right to acquire the same securities as if the holder had exercised its warrants. The warrants prohibit the Company from entering into specified transactions involving a change of control, unless the successor entity assumes all of the Company’s obligations under the warrants under a written agreement before the transaction is completed. When there is a transaction involving a permitted change of control, a holder of a warrant will have the right to force the Company to repurchase the holder’s warrant for a purchase price in cash equal to the Black-Scholes value (as calculated under the individual warrant agreements) of the then unexercised portion of the warrant.

Accounting for Warrants – The Company has determined that the warrants issued in the above transactions did not meet the conditions for classification in stockholders’ equity and as such, the Company has recorded them as a liability at fair value. The Company will revalue them at each reporting period. Further, as noted above, certain of the exercise prices declined as a result of the anti-dilution adjustments due to subsequent transactions. Accordingly, the Company recorded fair value adjustments quarterly, with total fair value adjustments of $35,260,000, $648,000 and $1,954,000 for the years ended December 31, 2014, 2013 and 2012, respectively, which is largely attributed to adjustment, if any, to their exercise prices, term shortening and changes in the market value of the Company’s common stock. See Note 12 for the Company’s fair value assumptions.

Registration Rights Agreements – In connection with the above issuances, the Company entered into a registration rights agreements with all of the investors to file registration statements on Form S-1 or S-3 with the Securities and Exchange Commission by certain dates for the resale by the purchasers of the shares of common stock issued and the shares of common stock issuable upon exercise of the warrants. Subject to customary grace periods, the Company is required to keep the registration statements (and the accompanying prospectuses) available for use for resale by the investors on a delayed or continuous basis at then-prevailing market prices at all times until the earlier of (i) the date as of which all of the investors may sell all of the shares of common stock required to be covered by the registration statement without restriction under Rule 144 under the Securities Act of 1933, as amended (including volume restrictions) and without the need for current public information required by Rule 144(c)(1), if applicable) or (ii) the date on which the investors have sold all of the shares of common stock covered by the registration statement. The Company must pay registration delay payments of up to 2% of each investor’s initial investment per month if the registration statement ceases to be effective prior to the expiration of deadlines provided for in the registration rights agreement. The initial registration statements became effective by the stated deadlines and the Company did not record any liability associated with any registration delay payments under the registration rights agreements.