* Investigators pressured researcher to pull talk on virus

* Talk was on origins and motives of Conficker Gang

LAS VEGAS, July 29 (Reuters) - Investigators searching for the criminals who infected millions of computers with the notorious Conficker virus are trying to limit access to information about its creators.

The investigators pressured one of the world’s leading experts in cybercrime to pull a talk on Conficker’s origins and motives of the gang behind the attack. He was due to discuss the topic on Thursday at the Black Hat security conference in Las Vegas, one of the world’s top forums for exchanging information on Internet threats

“I was asked not to go into that because of an ongoing investigation,” Mikko Hypponen, chief research officer for Internet security firm F-Secure, said in an interview on Wednesday.

He declined to say which agency requested him to pull the talk or explain why they asked him to do so.

Criminal investigators sometimes discourage people from disclosing sensitive information about crimes out of fear it might tip off suspects. Hypponen would not say if that was the reason.

Hypponen said he will still speak about Conficker at the conference, but "there will be no news" on the virus that attacks machines running Microsoft Corp's MSFT.O Windows operating system.

Conficker started spreading late last year and infected an estimated 10 million computers at its peak in March.

It was designed to let its creators turn compromised machines into “slaves” that respond to commands sent from a remote server that effectively controls an army of computers known as a botnet.

Security experts succeeding in cleaning up most infected PCs after an unprecedented public awareness campaign to clean it up. Hypponen said it now infects about 1 million PCs.

The Conficker botnet is one of many such networks controlled by syndicates that authorities believe are based in eastern Europe, Southeast Asia, China and Latin America. (Reporting by Jim Finkle; editing by Andre Grenon)