NEW YORK ( TheStreet) -- Pharmasset (Nasdaq: VRUS) is trading at unusually high volume Friday with 4.3 million shares changing hands. It is currently at 4.1 times its average daily volume and trading down $13.02 (-16.4%) at $66.38 as of 1:26 p.m. ET.

Pharmasset has a market cap of $5.9 billion and is part of the health care sector and drugs industry. Shares are up 260.6% year to date as of the close of trading on Thursday.

Pharmasset, Inc., a clinical-stage pharmaceutical company, focuses on discovering, developing, and commercializing novel drugs to treat viral infections.

TheStreet Ratings rates Pharmasset as a sell. The company's weaknesses can be seen in multiple areas, such as its deteriorating net income, weak operating cash flow and feeble growth in its earnings per share. You can view the full Pharmasset Ratings Report.

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