Facebook Inc (NASDAQ:FB) stock pulled back on Monday and continued to slide in early trading on Tuesday as investors considered the weight of ad-blocking software and whether it has the potential to take a significant bite out of its ad revenue. The social network is in combat with Adblock Plus in a battle a Princeton assistant professor says it can’t win.

Meanwhile analysts consider the various reasons sentiment on Facebook Inc (NASDAQ:FB) stock isn’t as strong as they think it could be.

Facebook (FB) stock impacted by ad blockers

This week the big issue affecting Facebook Inc (NASDAQ:FB) stock could be ad-blocking software. Wells Fargo analysts said this week that the social network’s move to beat down ad blockers on its desktop website indicates the size of the impact blockers have on it. Although ads on the desktop sites only generate about 15% of the company’s total ad revenue, Wells Fargo analysts said it appears as if ad blockers are starting to materially impact its results.

They pointed to Facebook’s most recent earnings report as evidence but added that the company is among the best-positioned in terms of being able to offset losses caused by ad blockers.

Can Facebook (FB) win the ad blocking war?

The social network said last week that it will change the way ads load on its desktop site so that it will be harder for ad blockers to detect them. However, Adblock Plus, the biggest ad blocker on the market, was quick to respond by making a small tweak to its settings to unravel Facebook’s latest efforts, explains the MIT Technology Review.

Princeton Assistant Professor Arvind Narayanan doesn’t believe the social network can win this war. He and undergraduate Grant Storey developed their own experimental ad “highlighter” to demonstrate this. It works as a plugin for Chrome, and when it is installed, Facebook News Feed adds are grayed out and the words “This is an ad” cover them.

Current ad blockers examine the HTML code that indicates to a Web browser which parts of a particular page are ads, and Facebook’s first move was simply to remove the HTML clues. However, the ad highlighter works differently by examining the areas of a page that humans can see and blocking posts that have the “Sponsored” tag. The reason this works better than blockers using HTML cues is because the Federal Trade Commission’s transparency rules requires the social network to clearly label ads.

Other reasons Facebook (FB) stock sentiment may be muted

JPMorgan analyst Doug Anmuth and team also considered some other reasons why investors may not be so keen on Facebook stock right now. They reiterated their Overweight rating and $170 price target on the stock in a report dated August 16 and outlined the biggest concerns they’ve been hearing from investors about it lately.

One has to do with mega cap growth and multiples, but they don’t believe Facebook Inc (NASDAQ:FB) stock will have similar multiple compression as other mega caps which have compressed by 60% to 80% from peak to trough growth. They expect the social network’s revenue to “decelerate at a measured pace as its ad ecosystem becomes more important & captures a greater share of marketer spend.”

Another issue some investors worry about is slowing ad load growth, but they explain that this isn’t surprising because it would have to happen at some point. Also management has been warning about it for some time, and they explain that ad load is becoming less and less important as a growth driver.

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Engagement also remains a concern due to small sequential declines in daily and monthly active users in some regions, but they say the ratio of daily to monthly active users is still steady at 66%.

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Also Facebook continues to take about 13% of U.S. mobile Internet minutes, excluding messenger and including tablets. This is two times greater than Snapchat, Twitter, Instagram and others combined, Anmuth and team explained.

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Investors are increasingly concerned about Snapchat, but the JPMorgan team doesn’t see it as much of a threat because they don’t believe it is really impacting engagement or ad revenue.

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Shares of Facebook Inc (NASDAQ:FB) stock edged downward by as much as 0.38% to $123.43 during regular trading hours on Tuesday.