The Soviet Union disappeared from the map more than two decades ago, but online an "evil empire" is thriving.

Security experts say the .su internet suffix assigned to the USSR in 1990 has turned into a haven for hackers who've flocked to the domain space to send spam and steal money.

Capitalist concerns rather than communist nostalgia explain the move.

"I don't think that this is really a political thing," said Oren David, a manager at the security firm RSA's anti-fraud unit. "It's all about business."

David and others said scammers began to move to .su after the administrators of Russia's .ru domain space toughened their rules in late 2011.

Group-IB, which runs one of Russia's two official internet watchdogs, said the number of malicious .su websites doubled in 2011 and again in 2012, surpassing the vast number of renegade sites on .ru and its newer Cyrillic-language counterpart.

The Soviet domain has lots of problems, Group-IB's Andrei Komarov said in a phone interview. "In my opinion more than half of cybercriminals in Russia and former USSR use it."

The most notorious site was Exposed.su, which purportedly published credit records belonging to Michelle Obama, the Republican presidential challengers Mitt Romney and Donald Trump, and celebrities including Britney Spears, Jay-Z, Beyoncé and Tiger Woods. The site is now defunct.

Other .su sites are used to control botnets, the networks of hijacked computers used to empty bank accounts, send spam and launch attacks against rival websites.

Internet hosting companies generally eliminate such sites as soon as they're identified, but Swiss security researcher Roman Huessy, whose abuse.ch blog tracks botnet control sites, said hackers based in the .su domain can operate with impunity for months at a time.

Asked for examples, he rattled off a series of sites actively working in the online equivalent of broad daylight, ransacking bank accounts and holding hard drives hostage in return for ransom.

"I can continue posting this list for ages," he said via Skype.

The history of .su goes back to the early days of the internet, when its architects were creating the country code suffixes intended to mark out a website's nationality. Some cold war-era domain names – such as .yu for Yugoslavia or .dd for East Germany – disappeared along with the countries to which they had been assigned. The .su domain, however, survived the dissolution of the Soviet Union in 1991 and the creation of the .ru domain in 1994, and has resisted repeated attempts to wipe it from the web because its operators refused to pull the plug on both commercial and patriotic grounds.

With more than 120,000 domains currently registered, mothballing .su now would be a messy operation.

"It's like blocking .com or .org," said Komarov. "Lots of legitimate domains are registered there."

Among them are stalin.su, which eulogises the former Soviet dictator and the English-language chronicle.su, an absurdist parody site.

Experts say, however, that many are fraudulent, and even the organisation behind .su accepts it has a problem on its hands.

"We realise it's a threat for our image," said Sergei Ovcharenko, whose Moscow-based non-profit Foundation for Internet Development took responsibility for .su in 2007.

Ovcharenko insisted that only a small number of .su sites were malicious, although he acknowledged that criminal sites can stay online for extremely long periods of time. He said his hands were tied by weak Russian legislation and outdated terms of service, but promised that stricter rules were on their way after months of legal legwork.

"We are almost there," he said. "This summer we'll be rolling out our new policy."

Meanwhile .su has become an increasingly notorious corner of the internet, an online echo of the "evil empire" moniker assigned to the Soviet Union by Ronald Reagan 30 years ago.

David, the RSA manager, said the emergence of a communist relic as a 21st century security threat was a bizarre blast from the past.

"I thought that the Berlin Wall and my grandma's borscht are the only remnants of the Soviet Union," he said. "I was wrong."