Users of Microsoft’s free email service Hotmail are reeling this week after a huge web security breach last month. All Hotmail users are encouraged to change their passwords and be vigilant as an increase in spam activity on the site has led to web security breaches.

Individual accounts have been hacked in recent weeks, and then the hacked accounts are then used to send spam to the entire contact list of the user. Victims have also reported that their email filter settings and other custom account features were changed following the breach.

“Hotmail is seeing instances of accounts being ‘hijacked’ by spammers who send emails out advertising an electronics website. The spam mails usually have subjects like ‘Good shopping good mood’ and may go to your contact list in addition to a random list of emails,” Rob Margel of Microsoft wrote on his blog.

The cyber criminals are not typically worried about changing the password as they only intend to use the account once or twice. They move quickly so that they can do as much damage as possible but want to jump around to avoid being caught. Changing the password is the only way to prevent further damage, passwords should be changed on a frequent basis to avoid problems such as this.

The origin of the malware is unknown, but the results are similar to phishing attacks that took place on Twitter a few months ago. The popular social networking site recently announced phishing attacks have become so frequent that it will now scan every link posted to the site for malware.