Typing the words “Jew” or “Jewish” in to any internet search engine turns up dozens of sites that feature vile material, most commonly divided into two categories – Holocaust denial and foaming-at-the-mouth madness about shadowy international conspiracies.
This is depressing enough in itself, but not nearly as depressing as the thought that countless people believe this hateful nonsense.
Depressing, too, that there is surely a link between this sort of material and the fact that the three synagogues near my home in Leeds all consider it necessary to have guards on the gates – sometimes bolstered by the police – when services are held.
This is where the anti-Semitism that proliferates online leads – to threats and violence.
Last year, the Community Security Trust, a charity that works with Britain’s Jewish community, recorded 1,382 anti-Semitic incidents – the highest number ever. Of those, 145 were assaults, up from 108 in 2016. The most common incidents were abuse being shouted in the street, and almost one in five involved the use of social media.
Worryingly, this may not be the true extent of the problem because the trust believes that there is “significant under-reporting” of incidents.
This is the context in which Labour’s turmoil over anti-Semitism must be seen.
It is not an abstract issue, confined to the ravings of hate-filled halfwits typing away on social media, but a real danger that results in people being attacked, abused and put in fear.
Anti-Semitism has particular resonance for Yorkshire and its Labour heritage. We are home to one of the largest Jewish communities in the country, and its links to the party have traditionally been strong.
The undoubted presence of anti-Semitism within Labour is an ugly stain on the name of a great political party, and the apparent inaction of Jeremy Corbyn to stamp it out among some of his most fervent followers calls into question his fitness to be its leader, let alone Prime Minister.
How deeply-rooted this hatred has become was underlined by the weekend’s reports that the 20 most pro-Corbyn Facebook groups contained thousands of anti-Semitic posts.
No previous Labour leader of modern times has faced such accusations of doing too little about anti-Semitism, yet they have swirled around Mr Corbyn ever since he won the leadership in 2015.
He has vehemently denied that he is anti-Semitic, and there is every reason to believe him. But protesting that this cancer within the party has nothing do with him isn’t good enough.
The fact remains that a virulent anti-Semitism has emerged on his watch among his fanatical grassroots support.
Expulsions have been few, and he has to say the least been careless in some of his associations on Facebook, particularly when he commented on the removal of a mural depicting a scene that could have come straight out of Nazi propaganda of the 1930s, so shockingly offensive were its crude stereotypes.
The problem for Mr Corbyn and Labour lies in the hard left’s hatred of Israel. Antipathy towards the Jewish state long ago mutated into anti-Semitism among some of his most devoted followers.
To stamp on them will alienate those most devoted to Mr Corbyn, who see him as one of their own.
Yet he must do so, and without delay, because the virulence of the disease within Labour ranks is little short of horrifying.
It was demonstrated last week when thousands of his supporters backed an open letter saying he was being attacked by a “very powerful special interest group”, which not only organised the rally in London to protest about Labour anti-Semitism, but also recruited the BBC to attack him.
And suddenly, we’re straight back to the lunacy of the more extreme websites with their wild allegations of a shadowy Jewish cabal pulling strings behind the scenes. It really is textbook anti-Semitism, at which the vast majority of decent Labour members and supporters must despair.
Even its own MPs are not spared abuse and threats, with Liverpool Wavertree MP Luciana Berger writing of the vicious anti-Semitism to which she has been subjected.
That tells us all we need to know about the depth of the problem, and how urgently Mr Corbyn needs to get a grip on the party and mercilessly throw out those peddling such inflammatory nonsense.
This has become much more than a matter of party management. This is now about clearing out hatred from one of the great institutions of British public life, and by doing so reinforcing the message of wider society that anti-Semitism is an abhorrence that will not be tolerated.
Mr Corbyn owes it to the good name of Labour to stamp out anti-Semitism in his party. More importantly, he owes it to his country too.