Antivirus vendor F-Secure has issued a warning for a new strain of the “Skulls” Trojan sneaking into Symbian-based smartphones by posing as a mobile security application. The latest mutant, identified as Skulls.L, pretends to be a pirated copy of the F-Secure Mobile Anti-Virus application, a sign that virus writers targeting cell phone users are borrowing well-known replication tactics from computer viruses.