The ratings of six internet and web service stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Marin Software, Inc.’s (MRIN) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). In Portfolio Grader’s specific subcategories of Equity and Cash Flow, MRIN also gets F’s. For more information, get Portfolio Grader’s complete analysis of MRIN stock.

Reis, Inc.’s (REIS) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Reis is engaged in the business of providing commercial real estate market information and analytical tools for its customers. The stock gets F’s in Earnings Momentum and Earnings Surprise. To get an in-depth look at REIS, get Portfolio Grader’s complete analysis of REIS stock.

Tremor Video, Inc.’s (TRMR) rating weakens this week, dropping to an F versus last week’s D. The stock gets F’s in Equity and Cash Flow. For more information, get Portfolio Grader’s complete analysis of TRMR stock.

This week, iPass’ (IPAS) rating worsens to an F from the company’s D rating a week ago. 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. The stock gets F’s in Earnings Revisions, Equity, Cash Flow and Sales Growth. To get an in-depth look at IPAS, get Portfolio Grader’s complete analysis of IPAS stock.

This week, Velti (VELT) drops from a D to an F rating. Velti is a global provider of mobile marketing and advertising solutions. The stock gets F’s in Earnings Growth and Earnings Momentum. For more information, get Portfolio Grader’s complete analysis of VELT stock.

Slipping from a C to a D rating, Channeladvisor Corporation (ECOM) takes a hit this week. The stock gets F’s in Equity and Cash Flow. As of Aug. 15, 2014, 16.2% of outstanding Channeladvisor Corporation shares were held short. To get an in-depth look at ECOM, get Portfolio Grader’s complete analysis of ECOM 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.