The hackers, reported to the SANS Institute's Internet Storm Center by a reader, also claim to be spamming 5 million people.
The Internet Storm Center did not disclose the URL the Russian hackers are using.
The hacker email read: "Dear Sir/Madam, Hello! We are internet hackers crew. We propose you for sale some interesting things: private exploits – stolen credit cards and bank accounts – we infect users' PCs with your trojan for low process (1,000 infected PCs for $25)."
The email goes on to boast: "You can use this hosting for any scam/fraud and nobody will close it...We are now spamming 5 million people, look out, the domain is alive as always and never gonna be down!"
Postini reported earlier this week that spam increased in February over its January mark in coincidence with the beginning of tax season in the U.S.
The company said it processed over 22 billion emails last month, blocking 14 billion of them. Spam comprised four billion of that number – an increase of 2 percent since January – the company said.