This week, the ratings of five Internet and Web Service stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

iPass (NASDAQ:IPAS) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. iPass offers enterprise mobility services on a global basis by providing services that simply, smartly and openly facilitate network access from mobile devices while providing the enterprise with visibility and control over their mobile ecosystem. In Portfolio Grader’s specific subcategories of Earnings Revisions, Equity, and Sales Growth, IPAS also gets an F. For a full analysis of IPAS stock, visit Portfolio Grader.

Liquidity Services (NASDAQ:LQDT) experiences a ratings drop this week, going from last week’s C to a D. Liquidity Services provides full service solutions to market and sell surplus assets and wholesale goods. The stock also gets an F in Earnings Momentum. The stock price has fallen 14.6% over the past month, worse than the 3.4% increase the Nasdaq has seen over the same period of time. As of March 28, 2013, 23.1% of outstanding Liquidity Services shares were held short. To get an in-depth look at LQDT, get Portfolio Grader’s complete analysis of LQDT stock.

Velti’s (NASDAQ:VELT) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Velti is a global provider of mobile marketing and advertising solutions. The stock gets F’s in Earnings Growth and Earnings Momentum. Wall Street appears to agree with the stock downgrade, with share prices dropping 49.5% over the past month. As of March 28, 2013, 26% of outstanding Velti shares were held short. For more information, get Portfolio Grader’s complete analysis of VELT stock.

Youku Tudou Inc. ADR (NYSE:YOKU) earns a D this week, moving down from last week’s grade of C. Youku.com operates as an Internet television company in the People’s Republic of China. The stock gets F’s in Earnings Revisions and Equity. Share prices fell 17.2% over the past month. For a full analysis of YOKU stock, visit Portfolio Grader.

This week, 21Vianet Group (NASDAQ:VNET) drops from C to a D rating. 21Vianet Group provides carrier-neutral Internet data center services in the People’s Republic of China. The stock gets F’s in Earnings Growth and Earnings Momentum. To get an in-depth look at VNET, get Portfolio Grader’s complete analysis of VNET stock.

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.