Cybercriminals are building country-specific botnets to target U.K. bank customers with dedicated malware, security company Trusteer Ltd. has reported.

The company identifies two pieces of malware -- the previously undetected Silon.var2 and the longer-established Agent.DBJP -- as the two bank Trojans being distributed by Zeus-based botnets using U.K.-infected PCs.

Silon.var2 now affects one in every 500 U.K.-based PCs connected to the Trusteer Flashlight system; that's 40 times higher than the rate of Silon.var2 infections detected in the U.S., according to Trusteer. Meanwhile, the security firm reports that Agent.DBJP affects one in every 5,000 U.K.-based PCs; again, that's a far higher rate of infection than Trusteer has detected in the U.S.

It's not clear whether these infection rates are partly a quirk of the Trusteer customer base, but it is clear that country-specific malware is now a defined strategy for the banking Trojan botnets, with the U.K. high on the hit list.

Although country-specific malware can apply to any country, the motivation for attacking banks and their customers in this way is to make detection harder. Global Trojan campaigns are easier to spot.

Full story: Computerworld