On January 25, 2018, the Company issued approximately 110,083 shares of common stock to a SNI Sellers for the conversion of approximately 110,083 shares of series B preferred shares.

On November 9, 2018 the Company issued 250,000 shares of common stock for the conversion of approximately 250,000 shares of Series B Convertible Preferred Stock, see Note 10.

Restricted Stock

During the nine months ended June 30, 2019 no restricted stock was granted or exercised. The restricted shares are to be earned over a three-year period and cliff vest at the end of the third year from the date of grant. Stock-based compensation expense attributable to restricted stock was $0.2 and $0.6 million, and $0.0 and $0.0 million for the three and nine months ended June 30, 2019 and 2018, respectively. As of June 30, 2019, there was approximately $1.6 million of unrecognized compensation expense related to restricted stock outstanding.

A summary of restricted stock activity is presented as follows:

Warrants

No warrants were granted or exercised during the nine months ended June 30, 2019.

Stock Options

As of June 30, 2019, there were stock options outstanding under the Company’s Second Amended and Restated 1997 Stock Option Plan and the Company’s Amended and Restated 2013 Incentive Stock Plan. Both plans were approved by the shareholders. The plans granted specified numbers of options to non-employee directors, and they authorized the Compensation Committee of the Board of Directors to grant either incentive or non-statutory stock options to employees. Vesting periods are established by the Compensation Committee at the time of grant. All stock options outstanding as of June 30, 2019 and September 30, 2018 were non-statutory stock options, had exercise prices equal to the market price on the date of grant, and had expiration dates ten years from the date of grant.

Stock-based compensation expense attributable to stock options and warrants was $0.3 million and $1.0 million, and 0.4 million and $1.0 million for the three and nine months ended June 30, 2019 and 2018, respectively. As of June 30, 2019 and June 30, 2018, there was approximately $1.9 million of unrecognized compensation expense related to unvested stock options outstanding each, and the weighted average vesting period for those options was 3.9 years. 

A summary of stock option activity is as follows:

The fair value of stock options granted was made using the Black-Scholes option pricing model and the following assumptions: