6. Common Shares

Share issuances

During the year ended December 31, 2015 and 2014, we issued 493,345 and 115,000 common shares, respectively, in connection with the vesting of RSUs.

Warrants

Warrant activity is summarized in the following table:


		Weighted		Weighted
		average		average
	Warrants	exercise price		remaining life
	outstanding	per share		(yrs.)	Intrinsic value
As of December 31, 2013	19,977,743	$	4.63	1.6	$	—
Expired (issued as part of equity financings completed in 2012)	(4,757,941)
As of December 31, 2014	15,219,802		5.00	0.8		—
Expired (issued as part of equity financing completed in 2010)	(15,219,802)
As of December 31, 2015	—	$	—	—	$	—

Stock-Based Compensation

Under our Stock Option Plan (the “Plan”) and our Long-Term Equity Incentive Plan (the “LTIP”), we may grant options and/or RSUs or restricted stock awards to our directors, officers, employees and consultants. The combined maximum number of our Common Shares that may be reserved for issuance under the Plan and the LTIP is a variable number equal to 10% of the issued and outstanding Common Shares on a non-diluted basis. Options and RSUs under the Plan and LTIP, respectively, are granted from time to time at the discretion of the Board, with vesting periods and other terms as determined by the Board. Stock-based compensation expense for the years ended December 31, 2015 and 2014 is as follows:


	Years Ended December 31,
	2015		2014
Stock options	$	8	$	160
Restricted stock units		809		966
	$	817	$	1,126

As of December 31, 2015, stock options and RSUs had unrecognized compensation expense of $23 and $440, respectively, which is expected to be recognized over a weighted average period of 3.0 and 1.13 years, respectively.

Stock Options

A summary of option activity under the Plan as of December 31, 2015 and 2014 and changes during the period then ended is set forth in the following table:


		Weighted average		Weighted average	Aggregate
	Number of	exercise price		remaining	intrinsic
	options	per option		contractual term	value
Outstanding - December 31, 2013	2,882,500	$	1.79	3.07	$	54
Granted	175,000		0.52
Cancelled/Forfeited	(125,000)		3.16
Expired	(675,000)		1.85
Outstanding - December 31, 2014	2,257,500		1.60	3.02		—
Outstanding - December 31, 2015	2,257,500	$	1.60	2.02	$	—

Exercisable - December 31, 2015	2,011,250	$	1.75	1.91	$	—

A summary of our unvested stock options as of December 31, 2015 and 2014 and changes during the period then ended is set forth in the following table:


				Weighted
		Weighted		average
		average		remaining
		grant-date		amortization
	Number of	fair value		period
	options	per option		(Years)
Unvested - December 31, 2013	738,750	$	0.22
Granted	175,000
Vested	(667,500)
Unvested - December 31, 2014	246,250		0.22
Unvested - December 31, 2015	246,250	$	0.22	3.00

The fair value of stock options granted during the year ended December 31, 2014 (no stock options were granted for the year ended December 31, 2015) to employees, directors and consultants was estimated at the grant date using the Black-Scholes option pricing model using the following assumptions:



Expected volatility	69.17	%
Risk-free interest rate	1.75	%
Expected life (years)	5
Dividend yield	N/A
Forfeiture assumption	10	%

Option pricing models require the input of highly subjective assumptions, including the expected price volatility. Expected price volatility is based on the historical volatility of our common shares. Changes in the subjective input assumptions can materially affect the fair value estimate. The expected term of the options granted represents the period of time that the options granted are expected to be outstanding. The risk-free rate for the periods within the contractual term of the option is based on the U.S. Treasury yield curve in effect at the date of grant.

Restricted Stock Units

The following table summarizes the RSU activity under the LTIP as of December 31, 2015 and 2014 and changes during the years then ended:


		Weighted average
	Number	grant-date fair
	of units	value per unit
Unvested - December 31, 2013	2,594,464	$	2.00
Cancelled/forfeited	(865,635)		3.42
Vested	(115,000)		3.84
Granted	2,079,000		0.46
Unvested - December 31, 2014	3,692,829	$	0.74
Cancelled/forfeited	(841,038)		0.73
Vested	(493,345)		1.62
Granted	1,727,000		0.27
Unvested - December 31, 2015	4,085,446	$	0.44

A portion of the RSU awards vest on a fixed future date provided the recipient continues to be affiliated with Vista on that date. Other RSU awards vest subject to certain performance and market criteria, including the accomplishment of certain corporate objectives and the Company’s share price performance. The vesting period for all RSUs is at least one year.

Weighted Average Common Shares


	At December 31,
	2015	2014
Basic common shares	82,571,182	82,294,331
Effect of dilutive stock-based awards	1,183,898	—
Diluted common shares	83,755,080	82,294,331

Stock options to purchase 2,257,500 and unvested RSUs representing 2,901,548 common shares were outstanding at December 31, 2015 but were not included in the computation of diluted weighted average common shares outstanding because their effect would have been anti-dilutive. Stock options to purchase 2,257,500 common shares, unvested RSUs representing 3,692,829 common shares, and warrants to purchase 15,219,802 common shares were outstanding at December 31, 2014 but were not included in the computation of diluted weighted average common shares outstanding because their effect would have been anti-dilutive.