This week, the overall grades of three Internet and Web Service stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Zix Corp. (NASDAQ:ZIXI) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Zix provides secure, Internet-based applications in a Software-as-a-Service (SaaS) model. In Portfolio Grader’s specific subcategory of Margin Growth, ZIXI also gets an F. The stock price has dropped 9.6% over the past month, worse than the 3% decrease the Nasdaq has seen over the same period of time. To get an in-depth look at ZIXI, get Portfolio Grader’s complete analysis of ZIXI stock.

Responsys (NASDAQ:MKTG) earns a D this week, moving down from last week’s grade of C. Responsys provides solutions to businesses in the retail, travel and hospitality, financial services, and high-technology sectors. The stock gets F’s in Earnings Growth and Margin Growth. The stock price has fallen 27.9% over the past month. The trailing PE Ratio for the stock is 31.20. For more information, get Portfolio Grader’s complete analysis of MKTG stock.

The rating of Velti (NASDAQ:VELT) slips from a C to a D. Velti is a global provider of mobile marketing and advertising solutions. The stock gets F’s in Earnings Growth, Earnings Momentum, and Earnings Revisions. Investors seem to agree with the downgrade and have pushed down the share price 50.7% over the past month. As of Nov. 23, 2012, 26.8% of outstanding Velti shares were held short. For a full analysis of VELT stock, visit Portfolio Grader.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.