Spammers are tricking users into opening malicious email attachments by promising them salacious pictures of female celebrities, security experts have warned.

The messages allegedly hold lewd images of the Hollywood actresses Angelina Jolie, Nicole Kidman, Milla Jovovich and Natalie Portman.

But, in fact this is intended to entice the recipient into clicking on a malicious attachment, which opens a zip file and infects the user’s computer. Once the program is activated it starts up an NTRootK-BY rootkit and installs a Trojan, which affects the Windows platform and installs more malware downloaded from the internet.

According to security researchers the emails usually arrive with an attached file entitled or

"These messages are masquerading as celebrity adult content, tempting the unwary into opening a file on their Windows computer which will install a rootkit and download further malicious code from the internet," said Graham Cluley, senior technology consultant for Sophos.

"This kind of social engineering trick is an effective way to fool many people into running code designed to allow hackers to break into computers," he added.