The volume of unsolicited email has jumped sharply over recent weeks as spammers target surfers with tax planning offers in the run up to the end of the financial year.

Newly published data from Postini, which processed over 22 billion emails in February, reported that 14 billion emails were identified as 'directory harvest attacks', 'malicious attacks' or 'email to invalid recipients'.

Spam emails totalled just over four billion, an increase of two per cent on January, bringing the total amount of spam quarantined to 73 per cent of all email for the month.

Spam was most prevalent on 18 February when 150 million messages were quarantined, accounting for 82 per cent of all messages stopped.

"The increase in spam was due to a rise in tax preparation offers and other financial service offerings that are more prevalent as we approach 15 April," said Andrew Lochart, senior director of marketing at Postini.

Legitimate email as a percentage of total SMTP connections remained virtually unchanged from January to February. Only 15.5 per cent of all messages were legitimate email.

Postini also filtered 2.2 million instant messaging conversations in February, stopping worms such as 'FakeMSN', 'Lamo.Worm' and 'Loxbot'.

Postini's measurements show that inbound Transport Layer Security (TLS) encryption volumes grew slightly from 6.5 per cent of all legitimate inbound traffic to seven per cent.

Outbound TLS volumes grew from 1.5 per cent of all messages to nearly three per cent, indicating users' continued adoption of encryption.

While spam was on the rise, email-borne viruses returned to their normal level of 1.5 per cent of all email in February. Postini said that it stopped over 40 million viruses.

Even the 'mywife' virus (aka 'kama sutra' or 'nyxem'), which on 3 February threatened to delete files on infected computers, ranked only eighth in Postini's top 10 viruses for the month.

Phishing emails in February totalled 2.8 million, 65 per cent lower than in January.