Experts are warning of a flood of emails distributed over the last few days purporting to contain pornographic images of celebrities.

The emails claim to have naked pictures of Nicole Kidman, Milla Jovovich, Angelina Jolie and Natalie Portman contained in a ZIP file. But when the file is opened it unpacks a NTRootK-BY rootkit and the Agent-FVT Trojan.

"These emails 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 nothing new – it's used so often by cybercriminals that it sometimes feels like it's been around since the days of the silent movies. However, that hasn't stopped it from being an effective way to fool many people into running code designed to allow hackers to break into computers."

Both pieces of malware will allow the creator full access to infected computers, which can then be used for spamming out more copies of the virus or slaved to take part in distributed denial of service attacks.

Computer users are being warned not to open attachments from strangers and to keep antivirus software updated daily.