Many people around the world are using Twitter for its marketing benefits, but according to some, a recent adjustment on the website might be shortchanging their search engine optimization (SEO).

According to AccuraCast, Twitter has begun placing a nofollow tag on all external links that users tweet. With so many Twitter users putting links in their messages, AccuraCast says this could give tweets a negligible search engine optimization (SEO) effect.

The news provider says there doesn’t seem to be a reason behind the addition of nofollow links – which are typically used to fight spam.

"[Twitter’s] justification for their decision is that it disuades spammers from abusing the service," says AccuraCast. "However, Twitter is quite good at stopping spammer accounts already. And, moreover, that doesn’t then explain why verified reliable accounts such as @Google and @stephenfry also have their links nofollowed." notes that until last week it was possible to still get links followed on Twitter by using Twitter API. However that loophole appears to be closed now.

Regardless of whether companies are getting credit for their links, more and more firms are using Twitter as a marketing tool. A recent report from Equation Research found that 71 percent of b2c companies say Twitter is part of their marketing.