Autorun-based threats, spread when users insert infected USB sticks without checking them for viruses, caused a whopping 12 percent of global infections in the first quarter of 2012. The threat persists even though the Autorun feature was eliminated from operating systems starting with Windows Vista SP1 in 2008.
“The magnitude of this threat - so many years after it should be extinct - is astonishing,” said Catalin Cosoi, Bitdefender’s Chief Security Researcher. “Some of the heavy-hitters of the virus world - such as Downadup and Stuxnet - spread this way. Prevention should be a simple matter.”
The mass introduction of USB storage devices and the apparition of the Autorun feature in Windows have been widely exploited since the early 2000s. Within five years, Autorun worms reached epidemic proportions, Autorun-based threats have dominated the malware landscape report since.
Five facts about Autorun-based malware:
1. The Autorun.inf file is not malicious itself. It is used by some families of malware that copy themselves on USB sticks to force the computer to automatically execute them when an infected stick is plugged into a Windows-based PC.
2. Among the most important families of malware that use the Autorun exploitation to spread are Stuxnet, Downadup, Sality, Rimecud or OnlineGames.
3. Autorun-based malware can copy itself on MP3/MP4 players, mobile phones, CF cards (such as those in digital cameras) and other devices. When plugged in other PCs, the malware is executed automatically.
4. Since autorun.inf files are plain-text files that can be opened and analysed, malware creators obfuscate their creations to make them unreadable by humans. However, this is also their weak point. This degree of obfuscation is uncommon in text files and triggers AV detection.
5. Trojan.AutorunInf (a detection that intercepts rogue autorun.inf files) has been the number one source of infection for more than three years in a row. During this time, it has helped various malware families infect millions of computers worldwide.