Spammers are using a phoney Google Chrome update to distribute a ransomware trojan, according to the security firm Malwarebytes.
Victims are sent a message ostensibly from the Google Security Team, informing users that their version of the web browser is out of date and linking them to a malware download.
If tricked by the scheme users then install the CTB Locker/Citrioni virus from a number of apparently compromised websites, with the malware then locking up the PC and blackmailing the user by promising to leave their files encrypted forever if they do not pay.
Writing in a blog post, Jerome Segura, senior security researcher at Malwarebytes, said: "The problem with ransomware is that while the active trojans can be removed, it is much more difficult and sometimes impossible to recover the encrypted files.
"Social engineering remains a powerful technique to trick people into running programs they shouldn’t," he added, referring to a range of manipulative techniques used by hackers to trick users into performing actions that will compromise their systems.
"As a rule of thumb you should always only download files from their official website rather than from some unknown site."
Copies of Citrioni have been available on black market hacker forums since at least last June, according to independent researcher Kafeine, and was initially targeted at Russian speakers before moving to English-speaking market.
Bitcoin payment is used by hacker to retain their anonymity, according to Malwarebytes, with the value of the ransom worth $500 (£330) and a time limit of 96 hours set before the files are permanently encrypted.