A computer virus called Cryptowall crippled the Durham Police Department’s computer system Friday morning. The virus was a kind of ransomware, which encrypts files, then tries to convince users to pay to decrypt them. Durham Town Manager Todd Selig says a Durham police officer opened what appeared to be a legitimate file attachment to an email on Thursday evening. By Friday morning, the entire computer system was taken off-line. Selig says the incident occurred Friday despite the fact that international law enforcement took down a previous version of the malware earlier this week. The department’s crime record system remains intact and unaffected by the virus. The computer system is expected to be back online Saturday.