Security software firm Kaspersky Lab says the mass mailing of MP3 spam is now a potential threat to users.
The spam circulating in MP3 files is so-called stock spam, which is designed to artificially increase the price of certain stocks by advertising them.
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The e-mails that Kaspersky Lab has detected do not contain any text. However, the attached MP3 file contains a recording which is between 25 and 33 seconds long.
If the user opens the file, they will hear a female voice advertising stocks in a company called Exit Only Inc a move on the part of spammers to inflate stock prices, and make a profit on subsequent sales of stock belonging to the advertised company.
This mass mailing appears to be a trial run on the part of the spammers, says Kaspersky, as the quality of the sound recording is poor, possibly an effort by the spammers to make the e-mails as small as possible.
Andrey Nikishin, director of Kaspersky Lab's IT security outsourcing operation, said, "Users often send each other short audio files with funny recordings - it seems as though spammers are banking on the fact that users think these files are worth listening to."