It may contain some passages judged by one Amazon customer to be "brilliantly written", but that isn't enough to spare Monica Byrne's The Girl in the Road a two-star kicking. The reason? Byrne has committed a political sin in presenting the scientific reality of climate change – or according to this customer "a fantasy future where it turned out that Global Warming fanatics actually got something right". Worse yet in this user's eyes, Byrne's depiction of women fighting back against male violence makes her guilty of misandry "thick enough to plow". Climate change and gender politics, two hot-button issues for reactionary conservatives who have found a new outlet for their hate speech – online reviews.

Negative book reviews are a reality of life for all professional writers. And the proliferation of user-generated reviews on sites such as Amazon and Goodreads make readers' opinions just as important as those of professional critics. But for authors like Byrne, politically motivated reviews are easy to spot. "There's an unmistakable tone," Byrne says. "And if they're using condescending or otherwise gender-coded language, that's a dead giveaway."

Byrne's debut novel was published with glowing blurbs from Kim Stanley Robinson and Neil Gaiman, making The Girl in the Road one of the most anticipated science-fiction novels of 2014. Byrne isn't intimidated by the trolls these endorsements have attracted, because their motivations are so clearly rooted in their own personal demons. "They feel threatened," Byrne suggests. "There's some deep bitterness that's unresolved in their lives, whether because of trauma or just laziness. Troll reviewing is a release for them."

This same release is at the heart of much online trolling. New cases of abusive behaviour towards women online appear all too often, with female bloggers and podcasters frequently bombarded with threats of violence and rape. It's a sad fact that this abuse is overwhelmingly directed at women, with many trolls speaking from the same textbook of reactionary political beliefs, often centred around spurious ideas of male biological superiority. But these commenters are far from superior. Unknown and anonymous, they lash out at successful women, as though abusive behaviour is their god-given right.

Over a 24-hour period, author and journalist Laurie Penny's new non-fiction book Unspeakable Things was bombarded with troll reviews that brought its rating on Amazon.co.uk down from 4.5 to only one star. The attack on Penny's work demonstrates a level of co-ordinated vindictiveness that makes trolls more than a petty annoyance. Following a tweet which declared "Let the trolling commence", a torrent of personal insults, personal attacks, threats of violence and rape fantasies were posted under the guise of book reviews on Amazon. Few, if any, of the trolls had read the book.

Sadly the experience is nothing new for Penny. Her incisive political commentary is often targeted by trolls, and like many high-profile women she faces a daily barrage of insults on social media which she puts down to "bigotry, boredom and a sense of powerlessness in their own lives". But trolling on a shopping site – particularly one so all-pervasive as Amazon – can have a direct economic impact. "Amazon ratings really do matter to booksellers and publishers," Penny says, "so attempts at sabotage like this are rather more effective than a stream of nasty comments under an article."

Unspeakable Things was saved from its one-star rating when Laurie Penny's readers stepped in to make their own voices heard against the din of whining trolls. The book currently has 199 reviews on Amazon, of which 81 are one stars and 104 five stars. It's an apt illustration of the divisive effect trolling has on public opinion, doing far more to strengthen the opinions it attacks than anything else. And as fantasy author Neil Gaiman commented on Twitter:

"Trolls give @pennyred's new book 1 star Amazon reviews. Other authors link in support & outrage. Book zooms up Amazon charts. #Bestrevenge."

The Nestle children's book prizewinner Matt Haig is another author who has spoken out against internet trolls. "Online trolls may be relatively new," he says, "but they often represent the groans and cries of a dying, less equal age." Haig's words are an important reminder that only a generation ago, many of the women writers attacked by men online would still have been trapped in the kind of "smiling servitude" lambasted by Germaine Greer in The Female Eunuch. Online abuse is, at its worst, a failed attempt to reassert old injustices.

"Trolling goes against everything good about the internet," Haig continues. "I love the way we, as a species, can now share thoughts and information. It brings us closer than ever before. The trolls remind us that our technology has upgraded but humanity hasn't – jealousy and bitterness are still there."