CryptoWall ransom Trojan has infected 625,000 systems, says Dell SecureWorks

Nevertheless, CryptoWall had still managed to encrypt a staggering 5.25 billion files, the firm said.

This will have been misery for the 1,683 victims Dell SecureWorks detected, most of which paid around the $500 mark in the folorn hope of receiving an unlock key. The ransoms also increased for some victims - 399 paid $1,000 with a single one coughing up an astonishing $10,000.

It'a also not clear whether Dell SecureWorks has found every payment server - a few weeks back, security firm PhishMe traced Bitcoin wallets containing more that $700,000-worth of currency.

It's worth remembering that although less successful than CryptLocker, since appearing in CryptoWall (also known as CryptoDefense) has managed to infect PCs in every country on earth.

The distribution has not been even, however. Of the infections detected by Dell SecureWorks, the US represented 40.6 percent (253,521), Vietnam 10.7 percent (66,590), the UK 40,258 (6.4 percent), Canada 5.2 percent (32,579), India with 5.2 percent (22,582), and Australia 3.1 percent (19,562).